From f3db548a3d068c051c4d6eba970b89422a6b9522 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Sun, 8 Jan 2023 19:23:00 -0500
Subject: [PATCH] AK+Everywhere: Rename FlyString to DeprecatedFlyString

DeprecatedFlyString relies heavily on DeprecatedString's StringImpl, so
let's rename it to A) match the name of DeprecatedString, B) write a new
FlyString class that is tied to String.
---
 AK/CMakeLists.txt                             |   2 +-
 AK/{FlyString.cpp => DeprecatedFlyString.cpp} |  52 +++----
 AK/{FlyString.h => DeprecatedFlyString.h}     |  34 ++---
 AK/DeprecatedString.cpp                       |   6 +-
 AK/DeprecatedString.h                         |   4 +-
 AK/Format.h                                   |   2 +-
 AK/Forward.h                                  |   4 +-
 AK/StringImpl.cpp                             |   4 +-
 AK/StringImpl.h                               |   2 +-
 AK/StringView.cpp                             |   4 +-
 AK/StringView.h                               |   4 +-
 Tests/AK/TestDeprecatedString.cpp             |  10 +-
 Userland/DevTools/Profiler/Profile.cpp        |   4 +-
 Userland/DevTools/Profiler/Profile.h          |  14 +-
 Userland/Libraries/LibAudio/FlacLoader.cpp    |   2 +-
 Userland/Libraries/LibAudio/LoaderError.h     |  10 +-
 Userland/Libraries/LibCpp/AST.h               |   6 +-
 Userland/Libraries/LibCpp/Preprocessor.h      |   4 +-
 Userland/Libraries/LibDebug/DebugInfo.cpp     |   4 +-
 Userland/Libraries/LibDebug/DebugInfo.h       |   2 +-
 .../Libraries/LibDebug/Dwarf/LineProgram.cpp  |   2 +-
 .../Libraries/LibDebug/Dwarf/LineProgram.h    |  10 +-
 .../Libraries/LibGfx/Font/FontDatabase.cpp    |   8 +-
 Userland/Libraries/LibGfx/Font/FontDatabase.h |   4 +-
 Userland/Libraries/LibGfx/Font/Typeface.h     |  10 +-
 Userland/Libraries/LibJS/AST.cpp              |  72 ++++-----
 Userland/Libraries/LibJS/AST.h                | 138 +++++++++---------
 .../Libraries/LibJS/Bytecode/ASTCodegen.cpp   |  24 +--
 .../Libraries/LibJS/Bytecode/Executable.h     |   6 +-
 .../Libraries/LibJS/Bytecode/Generator.cpp    |   8 +-
 Userland/Libraries/LibJS/Bytecode/Generator.h |  12 +-
 .../LibJS/Bytecode/IdentifierTable.cpp        |   4 +-
 .../LibJS/Bytecode/IdentifierTable.h          |   8 +-
 .../Libraries/LibJS/Bytecode/Interpreter.cpp  |   2 +-
 Userland/Libraries/LibJS/Interpreter.h        |   4 +-
 Userland/Libraries/LibJS/Lexer.cpp            |   4 +-
 Userland/Libraries/LibJS/Lexer.h              |   4 +-
 Userland/Libraries/LibJS/Module.cpp           |   4 +-
 Userland/Libraries/LibJS/Module.h             |  10 +-
 Userland/Libraries/LibJS/Parser.cpp           | 104 ++++++-------
 Userland/Libraries/LibJS/Parser.h             |   6 +-
 Userland/Libraries/LibJS/Print.cpp            |   2 +-
 .../LibJS/Runtime/AbstractOperations.cpp      |  12 +-
 .../LibJS/Runtime/AbstractOperations.h        |   2 +-
 .../Libraries/LibJS/Runtime/BoundFunction.h   |   4 +-
 .../LibJS/Runtime/CommonPropertyNames.h       |   2 +-
 Userland/Libraries/LibJS/Runtime/Completion.h |  14 +-
 .../LibJS/Runtime/DeclarativeEnvironment.cpp  |  18 +--
 .../LibJS/Runtime/DeclarativeEnvironment.h    |  28 ++--
 .../Runtime/ECMAScriptFunctionObject.cpp      |  20 +--
 .../LibJS/Runtime/ECMAScriptFunctionObject.h  |  12 +-
 .../Libraries/LibJS/Runtime/Environment.h     |  14 +-
 Userland/Libraries/LibJS/Runtime/Error.h      |   4 +-
 .../LibJS/Runtime/ExecutionContext.h          |   4 +-
 .../Libraries/LibJS/Runtime/FunctionObject.h  |   2 +-
 .../LibJS/Runtime/FunctionPrototype.h         |   4 +-
 .../LibJS/Runtime/GlobalEnvironment.cpp       |  28 ++--
 .../LibJS/Runtime/GlobalEnvironment.h         |  30 ++--
 .../LibJS/Runtime/ModuleEnvironment.cpp       |  10 +-
 .../LibJS/Runtime/ModuleEnvironment.h         |  14 +-
 .../LibJS/Runtime/ModuleNamespaceObject.cpp   |   4 +-
 .../LibJS/Runtime/ModuleNamespaceObject.h     |   6 +-
 .../Libraries/LibJS/Runtime/ModuleRequest.h   |  10 +-
 .../LibJS/Runtime/NativeFunction.cpp          |   6 +-
 .../Libraries/LibJS/Runtime/NativeFunction.h  |  16 +-
 Userland/Libraries/LibJS/Runtime/Object.cpp   |   6 +-
 .../LibJS/Runtime/ObjectEnvironment.cpp       |  14 +-
 .../LibJS/Runtime/ObjectEnvironment.h         |  14 +-
 .../LibJS/Runtime/PrivateEnvironment.cpp      |   4 +-
 .../LibJS/Runtime/PrivateEnvironment.h        |  12 +-
 .../Libraries/LibJS/Runtime/PropertyKey.h     |  12 +-
 .../Libraries/LibJS/Runtime/ProxyObject.cpp   |   2 +-
 .../Libraries/LibJS/Runtime/ProxyObject.h     |   2 +-
 .../Libraries/LibJS/Runtime/Reference.cpp     |   2 +-
 Userland/Libraries/LibJS/Runtime/Reference.h  |   4 +-
 .../LibJS/Runtime/RegExpPrototype.cpp         |   4 +-
 .../Libraries/LibJS/Runtime/StringOrSymbol.h  |  12 +-
 .../Libraries/LibJS/Runtime/TypedArray.cpp    |   2 +-
 Userland/Libraries/LibJS/Runtime/TypedArray.h |   4 +-
 .../LibJS/Runtime/TypedArrayConstructor.cpp   |   2 +-
 .../LibJS/Runtime/TypedArrayConstructor.h     |   2 +-
 Userland/Libraries/LibJS/Runtime/VM.cpp       |   8 +-
 Userland/Libraries/LibJS/Runtime/VM.h         |  10 +-
 .../Libraries/LibJS/Runtime/WrappedFunction.h |   2 +-
 Userland/Libraries/LibJS/SourceTextModule.cpp |  14 +-
 Userland/Libraries/LibJS/SourceTextModule.h   |   4 +-
 Userland/Libraries/LibJS/SyntheticModule.cpp  |  10 +-
 Userland/Libraries/LibJS/SyntheticModule.h    |  12 +-
 Userland/Libraries/LibJS/Token.h              |  16 +-
 Userland/Libraries/LibPDF/ColorSpace.cpp      |   6 +-
 Userland/Libraries/LibPDF/ColorSpace.h        |  12 +-
 Userland/Libraries/LibPDF/CommonNames.cpp     |   4 +-
 Userland/Libraries/LibPDF/CommonNames.h       |   6 +-
 Userland/Libraries/LibPDF/Document.cpp        |  10 +-
 Userland/Libraries/LibPDF/Document.h          |   8 +-
 Userland/Libraries/LibPDF/Filter.cpp          |   2 +-
 Userland/Libraries/LibPDF/Filter.h            |   4 +-
 Userland/Libraries/LibPDF/Fonts/PDFFont.cpp   |   2 +-
 Userland/Libraries/LibPDF/Object.h            |   2 +-
 .../Libraries/LibPDF/ObjectDerivatives.cpp    |  46 +++---
 Userland/Libraries/LibPDF/ObjectDerivatives.h |  26 ++--
 Userland/Libraries/LibPDF/Parser.cpp          |   4 +-
 Userland/Libraries/LibPDF/Renderer.cpp        |   2 +-
 Userland/Libraries/LibRegex/RegexMatch.h      |   6 +-
 Userland/Libraries/LibRegex/RegexParser.cpp   |   4 +-
 Userland/Libraries/LibRegex/RegexParser.h     |   6 +-
 .../LibVideo/Containers/Matroska/Document.h   |  14 +-
 .../LibWeb/Bindings/LegacyPlatformObject.cpp  |   2 +-
 .../LibWeb/Bindings/LegacyPlatformObject.h    |   2 +-
 .../LibWeb/Bindings/LocationObject.cpp        |   2 +-
 Userland/Libraries/LibWeb/CSS/FontFace.cpp    |   2 +-
 Userland/Libraries/LibWeb/CSS/FontFace.h      |  10 +-
 Userland/Libraries/LibWeb/CSS/MediaQuery.h    |   2 +-
 .../LibWeb/CSS/MediaQueryListEvent.cpp        |   4 +-
 .../LibWeb/CSS/MediaQueryListEvent.h          |   4 +-
 .../LibWeb/CSS/Parser/Declaration.cpp         |   2 +-
 .../Libraries/LibWeb/CSS/Parser/Declaration.h |   4 +-
 .../Libraries/LibWeb/CSS/Parser/Function.cpp  |   2 +-
 .../Libraries/LibWeb/CSS/Parser/Function.h    |   8 +-
 .../Libraries/LibWeb/CSS/Parser/Parser.cpp    |  12 +-
 Userland/Libraries/LibWeb/CSS/Parser/Rule.cpp |   2 +-
 Userland/Libraries/LibWeb/CSS/Parser/Rule.h   |   8 +-
 Userland/Libraries/LibWeb/CSS/Parser/Token.h  |   6 +-
 Userland/Libraries/LibWeb/CSS/Selector.h      |  20 +--
 .../Libraries/LibWeb/CSS/SelectorEngine.cpp   |   4 +-
 .../Libraries/LibWeb/CSS/StyleComputer.cpp    |  14 +-
 Userland/Libraries/LibWeb/CSS/StyleComputer.h |  10 +-
 Userland/Libraries/LibWeb/DOM/ARIAMixin.cpp   |   2 +-
 Userland/Libraries/LibWeb/DOM/ARIAMixin.h     |   6 +-
 .../Libraries/LibWeb/DOM/ARIARoleNames.cpp    |  16 +-
 Userland/Libraries/LibWeb/DOM/ARIARoleNames.h |  18 +--
 Userland/Libraries/LibWeb/DOM/Attr.cpp        |   2 +-
 Userland/Libraries/LibWeb/DOM/Attr.h          |  12 +-
 Userland/Libraries/LibWeb/DOM/CDATASection.h  |   2 +-
 Userland/Libraries/LibWeb/DOM/Comment.h       |   4 +-
 Userland/Libraries/LibWeb/DOM/CustomEvent.cpp |   6 +-
 Userland/Libraries/LibWeb/DOM/CustomEvent.h   |   6 +-
 .../Libraries/LibWeb/DOM/DOMEventListener.h   |   4 +-
 .../Libraries/LibWeb/DOM/DOMTokenList.cpp     |   4 +-
 Userland/Libraries/LibWeb/DOM/DOMTokenList.h  |   8 +-
 Userland/Libraries/LibWeb/DOM/Document.cpp    |   8 +-
 Userland/Libraries/LibWeb/DOM/Document.h      |  14 +-
 .../Libraries/LibWeb/DOM/DocumentFragment.h   |   4 +-
 Userland/Libraries/LibWeb/DOM/DocumentType.h  |   4 +-
 Userland/Libraries/LibWeb/DOM/Element.cpp     |  30 ++--
 Userland/Libraries/LibWeb/DOM/Element.h       |  50 +++----
 .../Libraries/LibWeb/DOM/ElementFactory.cpp   |   2 +-
 .../Libraries/LibWeb/DOM/ElementFactory.h     |   2 +-
 Userland/Libraries/LibWeb/DOM/Event.cpp       |   8 +-
 Userland/Libraries/LibWeb/DOM/Event.h         |  14 +-
 Userland/Libraries/LibWeb/DOM/EventTarget.cpp |  30 ++--
 Userland/Libraries/LibWeb/DOM/EventTarget.h   |  30 ++--
 .../Libraries/LibWeb/DOM/HTMLCollection.cpp   |   4 +-
 .../Libraries/LibWeb/DOM/HTMLCollection.h     |   6 +-
 .../Libraries/LibWeb/DOM/MutationRecord.cpp   |   4 +-
 .../Libraries/LibWeb/DOM/MutationRecord.h     |   8 +-
 .../Libraries/LibWeb/DOM/MutationType.cpp     |   2 +-
 Userland/Libraries/LibWeb/DOM/MutationType.h  |   4 +-
 .../Libraries/LibWeb/DOM/NamedNodeMap.cpp     |   2 +-
 Userland/Libraries/LibWeb/DOM/NamedNodeMap.h  |   2 +-
 Userland/Libraries/LibWeb/DOM/Node.cpp        |   4 +-
 Userland/Libraries/LibWeb/DOM/Node.h          |   6 +-
 .../LibWeb/DOM/NonElementParentNode.h         |   4 +-
 Userland/Libraries/LibWeb/DOM/ParentNode.cpp  |   4 +-
 Userland/Libraries/LibWeb/DOM/ParentNode.h    |   4 +-
 .../LibWeb/DOM/ProcessingInstruction.h        |   4 +-
 .../Libraries/LibWeb/DOM/QualifiedName.cpp    |   6 +-
 Userland/Libraries/LibWeb/DOM/QualifiedName.h |  18 +--
 Userland/Libraries/LibWeb/DOM/ShadowRoot.h    |   2 +-
 Userland/Libraries/LibWeb/DOM/Text.h          |   4 +-
 .../LibWeb/DOMParsing/XMLSerializer.cpp       |  34 ++---
 Userland/Libraries/LibWeb/Dump.cpp            |   2 +-
 .../Libraries/LibWeb/Encoding/TextDecoder.cpp |   6 +-
 .../Libraries/LibWeb/Encoding/TextDecoder.h   |   8 +-
 .../Libraries/LibWeb/Encoding/TextEncoder.cpp |   6 +-
 .../Libraries/LibWeb/Encoding/TextEncoder.h   |   2 +-
 Userland/Libraries/LibWeb/FontCache.h         |   4 +-
 .../Libraries/LibWeb/HTML/AttributeNames.cpp  |   4 +-
 .../Libraries/LibWeb/HTML/AttributeNames.h    |   6 +-
 Userland/Libraries/LibWeb/HTML/CloseEvent.cpp |   6 +-
 Userland/Libraries/LibWeb/HTML/CloseEvent.h   |   6 +-
 .../HTML/CrossOrigin/AbstractOperations.cpp   |   2 +-
 .../Libraries/LibWeb/HTML/DOMStringMap.cpp    |   2 +-
 Userland/Libraries/LibWeb/HTML/DOMStringMap.h |   2 +-
 Userland/Libraries/LibWeb/HTML/ErrorEvent.cpp |   6 +-
 Userland/Libraries/LibWeb/HTML/ErrorEvent.h   |   6 +-
 Userland/Libraries/LibWeb/HTML/EventNames.cpp |   2 +-
 Userland/Libraries/LibWeb/HTML/EventNames.h   |   4 +-
 .../LibWeb/HTML/GlobalEventHandlers.h         |   2 +-
 .../LibWeb/HTML/HTMLAnchorElement.cpp         |   4 +-
 .../Libraries/LibWeb/HTML/HTMLAnchorElement.h |   4 +-
 .../Libraries/LibWeb/HTML/HTMLAreaElement.cpp |   4 +-
 .../Libraries/LibWeb/HTML/HTMLAreaElement.h   |   4 +-
 .../Libraries/LibWeb/HTML/HTMLBaseElement.cpp |   2 +-
 .../Libraries/LibWeb/HTML/HTMLBaseElement.h   |   2 +-
 .../Libraries/LibWeb/HTML/HTMLBodyElement.cpp |   4 +-
 .../Libraries/LibWeb/HTML/HTMLBodyElement.h   |   6 +-
 .../Libraries/LibWeb/HTML/HTMLButtonElement.h |   2 +-
 .../Libraries/LibWeb/HTML/HTMLDataElement.h   |   2 +-
 .../LibWeb/HTML/HTMLDataListElement.h         |   2 +-
 .../LibWeb/HTML/HTMLDetailsElement.h          |   2 +-
 .../Libraries/LibWeb/HTML/HTMLDialogElement.h |   2 +-
 .../Libraries/LibWeb/HTML/HTMLDivElement.h    |   2 +-
 .../Libraries/LibWeb/HTML/HTMLElement.cpp     |   6 +-
 Userland/Libraries/LibWeb/HTML/HTMLElement.h  |   8 +-
 .../LibWeb/HTML/HTMLFieldSetElement.h         |   2 +-
 .../Libraries/LibWeb/HTML/HTMLFormElement.h   |   2 +-
 .../LibWeb/HTML/HTMLFrameSetElement.cpp       |   4 +-
 .../LibWeb/HTML/HTMLFrameSetElement.h         |   4 +-
 .../Libraries/LibWeb/HTML/HTMLHRElement.h     |   2 +-
 .../LibWeb/HTML/HTMLHeadingElement.h          |   2 +-
 .../Libraries/LibWeb/HTML/HTMLHtmlElement.h   |   2 +-
 .../LibWeb/HTML/HTMLIFrameElement.cpp         |   2 +-
 .../Libraries/LibWeb/HTML/HTMLIFrameElement.h |   2 +-
 .../LibWeb/HTML/HTMLImageElement.cpp          |   4 +-
 .../Libraries/LibWeb/HTML/HTMLImageElement.h  |   4 +-
 .../LibWeb/HTML/HTMLInputElement.cpp          |   6 +-
 .../Libraries/LibWeb/HTML/HTMLInputElement.h  |   6 +-
 .../Libraries/LibWeb/HTML/HTMLLIElement.h     |   2 +-
 .../Libraries/LibWeb/HTML/HTMLLinkElement.cpp |   4 +-
 .../Libraries/LibWeb/HTML/HTMLLinkElement.h   |   4 +-
 .../Libraries/LibWeb/HTML/HTMLMenuElement.h   |   2 +-
 .../Libraries/LibWeb/HTML/HTMLMeterElement.h  |   2 +-
 .../Libraries/LibWeb/HTML/HTMLModElement.cpp  |   2 +-
 .../Libraries/LibWeb/HTML/HTMLModElement.h    |   2 +-
 .../Libraries/LibWeb/HTML/HTMLOListElement.h  |   2 +-
 .../LibWeb/HTML/HTMLObjectElement.cpp         |   2 +-
 .../Libraries/LibWeb/HTML/HTMLObjectElement.h |   2 +-
 .../LibWeb/HTML/HTMLOptGroupElement.h         |   2 +-
 .../LibWeb/HTML/HTMLOptionElement.cpp         |   6 +-
 .../Libraries/LibWeb/HTML/HTMLOptionElement.h |   6 +-
 .../Libraries/LibWeb/HTML/HTMLOutputElement.h |   2 +-
 .../LibWeb/HTML/HTMLParagraphElement.h        |   2 +-
 .../Libraries/LibWeb/HTML/HTMLPreElement.h    |   2 +-
 .../LibWeb/HTML/HTMLProgressElement.h         |   2 +-
 .../LibWeb/HTML/HTMLQuoteElement.cpp          |   2 +-
 .../Libraries/LibWeb/HTML/HTMLQuoteElement.h  |   2 +-
 .../LibWeb/HTML/HTMLSelectElement.cpp         |   4 +-
 .../Libraries/LibWeb/HTML/HTMLSelectElement.h |   4 +-
 .../Libraries/LibWeb/HTML/HTMLSpanElement.h   |   2 +-
 .../LibWeb/HTML/HTMLTableCaptionElement.h     |   2 +-
 .../LibWeb/HTML/HTMLTableCellElement.cpp      |   2 +-
 .../LibWeb/HTML/HTMLTableCellElement.h        |   2 +-
 .../Libraries/LibWeb/HTML/HTMLTableElement.h  |   2 +-
 .../LibWeb/HTML/HTMLTableRowElement.h         |   2 +-
 .../LibWeb/HTML/HTMLTableSectionElement.h     |   2 +-
 .../LibWeb/HTML/HTMLTextAreaElement.h         |   2 +-
 .../Libraries/LibWeb/HTML/HTMLTimeElement.h   |   2 +-
 .../Libraries/LibWeb/HTML/HTMLUListElement.h  |   2 +-
 .../Libraries/LibWeb/HTML/MessageEvent.cpp    |   6 +-
 Userland/Libraries/LibWeb/HTML/MessageEvent.h |   6 +-
 .../LibWeb/HTML/PageTransitionEvent.cpp       |   6 +-
 .../LibWeb/HTML/PageTransitionEvent.h         |   6 +-
 .../LibWeb/HTML/Parser/HTMLParser.cpp         |  10 +-
 .../Libraries/LibWeb/HTML/Parser/HTMLParser.h |   8 +-
 .../Libraries/LibWeb/HTML/Parser/HTMLToken.h  |  20 +--
 .../Parser/ListOfActiveFormattingElements.cpp |   2 +-
 .../Parser/ListOfActiveFormattingElements.h   |   2 +-
 .../HTML/Parser/StackOfOpenElements.cpp       |  22 +--
 .../LibWeb/HTML/Parser/StackOfOpenElements.h  |  20 +--
 .../LibWeb/HTML/PromiseRejectionEvent.cpp     |   6 +-
 .../LibWeb/HTML/PromiseRejectionEvent.h       |   6 +-
 .../Libraries/LibWeb/HTML/SubmitEvent.cpp     |   6 +-
 Userland/Libraries/LibWeb/HTML/SubmitEvent.h  |   6 +-
 Userland/Libraries/LibWeb/HTML/TagNames.cpp   |   2 +-
 Userland/Libraries/LibWeb/HTML/TagNames.h     |   4 +-
 Userland/Libraries/LibWeb/HTML/Window.cpp     |   2 +-
 Userland/Libraries/LibWeb/HTML/Window.h       |   4 +-
 Userland/Libraries/LibWeb/HTML/Worker.cpp     |   4 +-
 Userland/Libraries/LibWeb/HTML/Worker.h       |   8 +-
 Userland/Libraries/LibWeb/Namespace.cpp       |   2 +-
 Userland/Libraries/LibWeb/Namespace.h         |   4 +-
 .../Libraries/LibWeb/Page/EventHandler.cpp    |   2 +-
 Userland/Libraries/LibWeb/Page/EventHandler.h |   2 +-
 .../Libraries/LibWeb/SVG/AttributeNames.cpp   |   2 +-
 .../Libraries/LibWeb/SVG/AttributeNames.h     |   4 +-
 .../Libraries/LibWeb/SVG/SVGCircleElement.cpp |   2 +-
 .../Libraries/LibWeb/SVG/SVGCircleElement.h   |   2 +-
 .../LibWeb/SVG/SVGEllipseElement.cpp          |   2 +-
 .../Libraries/LibWeb/SVG/SVGEllipseElement.h  |   2 +-
 .../Libraries/LibWeb/SVG/SVGLineElement.cpp   |   2 +-
 .../Libraries/LibWeb/SVG/SVGLineElement.h     |   2 +-
 .../Libraries/LibWeb/SVG/SVGPathElement.cpp   |   2 +-
 .../Libraries/LibWeb/SVG/SVGPathElement.h     |   2 +-
 .../LibWeb/SVG/SVGPolygonElement.cpp          |   2 +-
 .../Libraries/LibWeb/SVG/SVGPolygonElement.h  |   2 +-
 .../LibWeb/SVG/SVGPolylineElement.cpp         |   2 +-
 .../Libraries/LibWeb/SVG/SVGPolylineElement.h |   2 +-
 .../Libraries/LibWeb/SVG/SVGRectElement.cpp   |   2 +-
 .../Libraries/LibWeb/SVG/SVGRectElement.h     |   2 +-
 .../Libraries/LibWeb/SVG/SVGSVGElement.cpp    |   2 +-
 Userland/Libraries/LibWeb/SVG/SVGSVGElement.h |   2 +-
 Userland/Libraries/LibWeb/SVG/TagNames.cpp    |   2 +-
 Userland/Libraries/LibWeb/SVG/TagNames.h      |   4 +-
 .../Libraries/LibWeb/UIEvents/EventNames.cpp  |   2 +-
 .../Libraries/LibWeb/UIEvents/EventNames.h    |   4 +-
 .../Libraries/LibWeb/UIEvents/FocusEvent.cpp  |   4 +-
 .../Libraries/LibWeb/UIEvents/FocusEvent.h    |   4 +-
 .../LibWeb/UIEvents/KeyboardEvent.cpp         |   8 +-
 .../Libraries/LibWeb/UIEvents/KeyboardEvent.h |   8 +-
 .../Libraries/LibWeb/UIEvents/MouseEvent.cpp  |   6 +-
 .../Libraries/LibWeb/UIEvents/MouseEvent.h    |   6 +-
 .../Libraries/LibWeb/UIEvents/UIEvent.cpp     |   8 +-
 Userland/Libraries/LibWeb/UIEvents/UIEvent.h  |   8 +-
 .../Libraries/LibWeb/UIEvents/WheelEvent.cpp  |   6 +-
 .../Libraries/LibWeb/UIEvents/WheelEvent.h    |   6 +-
 .../LibWeb/WebGL/WebGLContextEvent.cpp        |   6 +-
 .../LibWeb/WebGL/WebGLContextEvent.h          |   6 +-
 .../LibWeb/WebGL/WebGLRenderingContext.cpp    |   2 +-
 .../Libraries/LibWeb/WebIDL/DOMException.cpp  |   6 +-
 .../Libraries/LibWeb/WebIDL/DOMException.h    |  32 ++--
 Userland/Libraries/LibWeb/XHR/EventNames.cpp  |   2 +-
 Userland/Libraries/LibWeb/XHR/EventNames.h    |   4 +-
 .../Libraries/LibWeb/XHR/ProgressEvent.cpp    |   6 +-
 Userland/Libraries/LibWeb/XHR/ProgressEvent.h |   6 +-
 .../LibWeb/XML/XMLDocumentBuilder.cpp         |   2 +-
 316 files changed, 1177 insertions(+), 1177 deletions(-)
 rename AK/{FlyString.cpp => DeprecatedFlyString.cpp} (54%)
 rename AK/{FlyString.h => DeprecatedFlyString.h} (69%)

diff --git a/AK/CMakeLists.txt b/AK/CMakeLists.txt
index 64051dac995..778593085eb 100644
--- a/AK/CMakeLists.txt
+++ b/AK/CMakeLists.txt
@@ -2,9 +2,9 @@ set(AK_SOURCES
     Assertions.cpp
     Base64.cpp
     CircularBuffer.cpp
+    DeprecatedFlyString.cpp
     DeprecatedString.cpp
     FloatingPointStringConversions.cpp
-    FlyString.cpp
     Format.cpp
     FuzzyMatch.cpp
     GenericLexer.cpp
diff --git a/AK/FlyString.cpp b/AK/DeprecatedFlyString.cpp
similarity index 54%
rename from AK/FlyString.cpp
rename to AK/DeprecatedFlyString.cpp
index 5dcd6ea9284..1d437702896 100644
--- a/AK/FlyString.cpp
+++ b/AK/DeprecatedFlyString.cpp
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashTable.h>
 #include <AK/Optional.h>
 #include <AK/Singleton.h>
@@ -14,7 +14,7 @@
 
 namespace AK {
 
-struct FlyStringImplTraits : public Traits<StringImpl*> {
+struct DeprecatedFlyStringImplTraits : public Traits<StringImpl*> {
     static unsigned hash(StringImpl const* s) { return s ? s->hash() : 0; }
     static bool equals(StringImpl const* a, StringImpl const* b)
     {
@@ -24,19 +24,19 @@ struct FlyStringImplTraits : public Traits<StringImpl*> {
     }
 };
 
-static Singleton<HashTable<StringImpl*, FlyStringImplTraits>> s_table;
+static Singleton<HashTable<StringImpl*, DeprecatedFlyStringImplTraits>> s_table;
 
-static HashTable<StringImpl*, FlyStringImplTraits>& fly_impls()
+static HashTable<StringImpl*, DeprecatedFlyStringImplTraits>& fly_impls()
 {
     return *s_table;
 }
 
-void FlyString::did_destroy_impl(Badge<StringImpl>, StringImpl& impl)
+void DeprecatedFlyString::did_destroy_impl(Badge<StringImpl>, StringImpl& impl)
 {
     fly_impls().remove(&impl);
 }
 
-FlyString::FlyString(DeprecatedString const& string)
+DeprecatedFlyString::DeprecatedFlyString(DeprecatedString const& string)
 {
     if (string.is_null())
         return;
@@ -55,7 +55,7 @@ FlyString::FlyString(DeprecatedString const& string)
     }
 }
 
-FlyString::FlyString(StringView string)
+DeprecatedFlyString::DeprecatedFlyString(StringView string)
 {
     if (string.is_null())
         return;
@@ -74,70 +74,70 @@ FlyString::FlyString(StringView string)
 }
 
 template<typename T>
-Optional<T> FlyString::to_int(TrimWhitespace trim_whitespace) const
+Optional<T> DeprecatedFlyString::to_int(TrimWhitespace trim_whitespace) const
 {
     return StringUtils::convert_to_int<T>(view(), trim_whitespace);
 }
 
-template Optional<i8> FlyString::to_int(TrimWhitespace) const;
-template Optional<i16> FlyString::to_int(TrimWhitespace) const;
-template Optional<i32> FlyString::to_int(TrimWhitespace) const;
-template Optional<i64> FlyString::to_int(TrimWhitespace) const;
+template Optional<i8> DeprecatedFlyString::to_int(TrimWhitespace) const;
+template Optional<i16> DeprecatedFlyString::to_int(TrimWhitespace) const;
+template Optional<i32> DeprecatedFlyString::to_int(TrimWhitespace) const;
+template Optional<i64> DeprecatedFlyString::to_int(TrimWhitespace) const;
 
 template<typename T>
-Optional<T> FlyString::to_uint(TrimWhitespace trim_whitespace) const
+Optional<T> DeprecatedFlyString::to_uint(TrimWhitespace trim_whitespace) const
 {
     return StringUtils::convert_to_uint<T>(view(), trim_whitespace);
 }
 
-template Optional<u8> FlyString::to_uint(TrimWhitespace) const;
-template Optional<u16> FlyString::to_uint(TrimWhitespace) const;
-template Optional<u32> FlyString::to_uint(TrimWhitespace) const;
-template Optional<u64> FlyString::to_uint(TrimWhitespace) const;
+template Optional<u8> DeprecatedFlyString::to_uint(TrimWhitespace) const;
+template Optional<u16> DeprecatedFlyString::to_uint(TrimWhitespace) const;
+template Optional<u32> DeprecatedFlyString::to_uint(TrimWhitespace) const;
+template Optional<u64> DeprecatedFlyString::to_uint(TrimWhitespace) const;
 
 #ifndef KERNEL
-Optional<double> FlyString::to_double(TrimWhitespace trim_whitespace) const
+Optional<double> DeprecatedFlyString::to_double(TrimWhitespace trim_whitespace) const
 {
     return StringUtils::convert_to_floating_point<double>(view(), trim_whitespace);
 }
 
-Optional<float> FlyString::to_float(TrimWhitespace trim_whitespace) const
+Optional<float> DeprecatedFlyString::to_float(TrimWhitespace trim_whitespace) const
 {
     return StringUtils::convert_to_floating_point<float>(view(), trim_whitespace);
 }
 #endif
 
-bool FlyString::equals_ignoring_case(StringView other) const
+bool DeprecatedFlyString::equals_ignoring_case(StringView other) const
 {
     return StringUtils::equals_ignoring_case(view(), other);
 }
 
-bool FlyString::starts_with(StringView str, CaseSensitivity case_sensitivity) const
+bool DeprecatedFlyString::starts_with(StringView str, CaseSensitivity case_sensitivity) const
 {
     return StringUtils::starts_with(view(), str, case_sensitivity);
 }
 
-bool FlyString::ends_with(StringView str, CaseSensitivity case_sensitivity) const
+bool DeprecatedFlyString::ends_with(StringView str, CaseSensitivity case_sensitivity) const
 {
     return StringUtils::ends_with(view(), str, case_sensitivity);
 }
 
-FlyString FlyString::to_lowercase() const
+DeprecatedFlyString DeprecatedFlyString::to_lowercase() const
 {
     return DeprecatedString(*m_impl).to_lowercase();
 }
 
-bool FlyString::operator==(DeprecatedString const& other) const
+bool DeprecatedFlyString::operator==(DeprecatedString const& other) const
 {
     return m_impl == other.impl() || view() == other.view();
 }
 
-bool FlyString::operator==(StringView string) const
+bool DeprecatedFlyString::operator==(StringView string) const
 {
     return view() == string;
 }
 
-bool FlyString::operator==(char const* string) const
+bool DeprecatedFlyString::operator==(char const* string) const
 {
     return view() == string;
 }
diff --git a/AK/FlyString.h b/AK/DeprecatedFlyString.h
similarity index 69%
rename from AK/FlyString.h
rename to AK/DeprecatedFlyString.h
index 74e18dbb8da..513cbc3134d 100644
--- a/AK/FlyString.h
+++ b/AK/DeprecatedFlyString.h
@@ -11,39 +11,39 @@
 
 namespace AK {
 
-class FlyString {
+class DeprecatedFlyString {
 public:
-    FlyString() = default;
-    FlyString(FlyString const& other)
+    DeprecatedFlyString() = default;
+    DeprecatedFlyString(DeprecatedFlyString const& other)
         : m_impl(other.impl())
     {
     }
-    FlyString(FlyString&& other)
+    DeprecatedFlyString(DeprecatedFlyString&& other)
         : m_impl(move(other.m_impl))
     {
     }
-    FlyString(DeprecatedString const&);
-    FlyString(StringView);
-    FlyString(char const* string)
-        : FlyString(static_cast<DeprecatedString>(string))
+    DeprecatedFlyString(DeprecatedString const&);
+    DeprecatedFlyString(StringView);
+    DeprecatedFlyString(char const* string)
+        : DeprecatedFlyString(static_cast<DeprecatedString>(string))
     {
     }
 
-    static FlyString from_fly_impl(NonnullRefPtr<StringImpl> impl)
+    static DeprecatedFlyString from_fly_impl(NonnullRefPtr<StringImpl> impl)
     {
         VERIFY(impl->is_fly());
-        FlyString string;
+        DeprecatedFlyString string;
         string.m_impl = move(impl);
         return string;
     }
 
-    FlyString& operator=(FlyString const& other)
+    DeprecatedFlyString& operator=(DeprecatedFlyString const& other)
     {
         m_impl = other.m_impl;
         return *this;
     }
 
-    FlyString& operator=(FlyString&& other)
+    DeprecatedFlyString& operator=(DeprecatedFlyString&& other)
     {
         m_impl = move(other.m_impl);
         return *this;
@@ -52,7 +52,7 @@ public:
     bool is_empty() const { return !m_impl || !m_impl->length(); }
     bool is_null() const { return !m_impl; }
 
-    bool operator==(FlyString const& other) const { return m_impl == other.m_impl; }
+    bool operator==(DeprecatedFlyString const& other) const { return m_impl == other.m_impl; }
 
     bool operator==(DeprecatedString const&) const;
 
@@ -67,7 +67,7 @@ public:
     ALWAYS_INLINE u32 hash() const { return m_impl ? m_impl->existing_hash() : 0; }
     ALWAYS_INLINE StringView view() const { return m_impl ? m_impl->view() : StringView {}; }
 
-    FlyString to_lowercase() const;
+    DeprecatedFlyString to_lowercase() const;
 
     template<typename T = int>
     Optional<T> to_int(TrimWhitespace = TrimWhitespace::Yes) const;
@@ -95,12 +95,12 @@ private:
 };
 
 template<>
-struct Traits<FlyString> : public GenericTraits<FlyString> {
-    static unsigned hash(FlyString const& s) { return s.hash(); }
+struct Traits<DeprecatedFlyString> : public GenericTraits<DeprecatedFlyString> {
+    static unsigned hash(DeprecatedFlyString const& s) { return s.hash(); }
 };
 
 }
 
 #if USING_AK_GLOBALLY
-using AK::FlyString;
+using AK::DeprecatedFlyString;
 #endif
diff --git a/AK/DeprecatedString.cpp b/AK/DeprecatedString.cpp
index a929824ea37..957dc3d675a 100644
--- a/AK/DeprecatedString.cpp
+++ b/AK/DeprecatedString.cpp
@@ -5,8 +5,8 @@
  */
 
 #include <AK/ByteBuffer.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Format.h>
 #include <AK/Function.h>
 #include <AK/StdLibExtras.h>
@@ -15,7 +15,7 @@
 
 namespace AK {
 
-bool DeprecatedString::operator==(FlyString const& fly_string) const
+bool DeprecatedString::operator==(DeprecatedFlyString const& fly_string) const
 {
     return m_impl == fly_string.impl() || view() == fly_string.view();
 }
@@ -375,7 +375,7 @@ DeprecatedString escape_html_entities(StringView html)
     return builder.to_deprecated_string();
 }
 
-DeprecatedString::DeprecatedString(FlyString const& string)
+DeprecatedString::DeprecatedString(DeprecatedFlyString const& string)
     : m_impl(string.impl())
 {
 }
diff --git a/AK/DeprecatedString.h b/AK/DeprecatedString.h
index c126f2c21ac..f9e09ae0f1f 100644
--- a/AK/DeprecatedString.h
+++ b/AK/DeprecatedString.h
@@ -93,7 +93,7 @@ public:
     {
     }
 
-    DeprecatedString(FlyString const&);
+    DeprecatedString(DeprecatedFlyString const&);
 
     [[nodiscard]] static DeprecatedString repeated(char, size_t count);
     [[nodiscard]] static DeprecatedString repeated(StringView, size_t count);
@@ -212,7 +212,7 @@ public:
 
     bool operator==(StringView) const;
 
-    bool operator==(FlyString const&) const;
+    bool operator==(DeprecatedFlyString const&) const;
 
     bool operator<(DeprecatedString const&) const;
     bool operator<(char const*) const;
diff --git a/AK/Format.h b/AK/Format.h
index cb35323e609..a7a1080b9b5 100644
--- a/AK/Format.h
+++ b/AK/Format.h
@@ -461,7 +461,7 @@ template<>
 struct Formatter<DeprecatedString> : Formatter<StringView> {
 };
 template<>
-struct Formatter<FlyString> : Formatter<StringView> {
+struct Formatter<DeprecatedFlyString> : Formatter<StringView> {
 };
 
 template<typename T>
diff --git a/AK/Forward.h b/AK/Forward.h
index 3803009a4ae..6805f659b12 100644
--- a/AK/Forward.h
+++ b/AK/Forward.h
@@ -27,13 +27,13 @@ class JsonArray;
 class JsonObject;
 class JsonValue;
 class StackInfo;
+class DeprecatedFlyString;
 class DeprecatedString;
 class StringBuilder;
 class StringImpl;
 class StringView;
 class Time;
 class URL;
-class FlyString;
 class String;
 class Utf16View;
 class Utf32View;
@@ -160,6 +160,7 @@ using AK::Bytes;
 using AK::CircularBuffer;
 using AK::CircularDuplexStream;
 using AK::CircularQueue;
+using AK::DeprecatedFlyString;
 using AK::DeprecatedString;
 using AK::DoublyLinkedList;
 using AK::DuplexMemoryStream;
@@ -167,7 +168,6 @@ using AK::Error;
 using AK::ErrorOr;
 using AK::FixedArray;
 using AK::FixedPoint;
-using AK::FlyString;
 using AK::Function;
 using AK::GenericLexer;
 using AK::HashMap;
diff --git a/AK/StringImpl.cpp b/AK/StringImpl.cpp
index 76cc66e431f..56f2cc73de7 100644
--- a/AK/StringImpl.cpp
+++ b/AK/StringImpl.cpp
@@ -5,7 +5,7 @@
  */
 
 #include <AK/CharacterTypes.h>
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/HashTable.h>
 #include <AK/StringHash.h>
 #include <AK/StringImpl.h>
@@ -32,7 +32,7 @@ StringImpl::StringImpl(ConstructWithInlineBufferTag, size_t length)
 StringImpl::~StringImpl()
 {
     if (m_fly)
-        FlyString::did_destroy_impl({}, *this);
+        DeprecatedFlyString::did_destroy_impl({}, *this);
 }
 
 NonnullRefPtr<StringImpl> StringImpl::create_uninitialized(size_t length, char*& buffer)
diff --git a/AK/StringImpl.h b/AK/StringImpl.h
index 85ad9d62aee..00b40812b53 100644
--- a/AK/StringImpl.h
+++ b/AK/StringImpl.h
@@ -78,7 +78,7 @@ public:
     unsigned case_insensitive_hash() const;
 
     bool is_fly() const { return m_fly; }
-    void set_fly(Badge<FlyString>, bool fly) const { m_fly = fly; }
+    void set_fly(Badge<DeprecatedFlyString>, bool fly) const { m_fly = fly; }
 
 private:
     enum ConstructTheEmptyStringImplTag {
diff --git a/AK/StringView.cpp b/AK/StringView.cpp
index 8d907e4d858..1d8e6fe1520 100644
--- a/AK/StringView.cpp
+++ b/AK/StringView.cpp
@@ -13,8 +13,8 @@
 #include <AK/Vector.h>
 
 #ifndef KERNEL
+#    include <AK/DeprecatedFlyString.h>
 #    include <AK/DeprecatedString.h>
-#    include <AK/FlyString.h>
 #    include <AK/String.h>
 #endif
 
@@ -33,7 +33,7 @@ StringView::StringView(DeprecatedString const& string)
 {
 }
 
-StringView::StringView(FlyString const& string)
+StringView::StringView(DeprecatedFlyString const& string)
     : m_characters(string.characters())
     , m_length(string.length())
 {
diff --git a/AK/StringView.h b/AK/StringView.h
index 7cbc760af9c..7fd23ef3333 100644
--- a/AK/StringView.h
+++ b/AK/StringView.h
@@ -50,14 +50,14 @@ public:
 #ifndef KERNEL
     StringView(String const&);
     StringView(DeprecatedString const&);
-    StringView(FlyString const&);
+    StringView(DeprecatedFlyString const&);
 #endif
 
     explicit StringView(ByteBuffer&&) = delete;
 #ifndef KERNEL
     explicit StringView(String&&) = delete;
     explicit StringView(DeprecatedString&&) = delete;
-    explicit StringView(FlyString&&) = delete;
+    explicit StringView(DeprecatedFlyString&&) = delete;
 #endif
 
     [[nodiscard]] constexpr bool is_null() const
diff --git a/Tests/AK/TestDeprecatedString.cpp b/Tests/AK/TestDeprecatedString.cpp
index 0502df68385..6442379642e 100644
--- a/Tests/AK/TestDeprecatedString.cpp
+++ b/Tests/AK/TestDeprecatedString.cpp
@@ -6,8 +6,8 @@
 
 #include <LibTest/TestCase.h>
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/StringBuilder.h>
 #include <AK/Vector.h>
 #include <cstring>
@@ -145,18 +145,18 @@ TEST_CASE(to_uppercase)
 TEST_CASE(flystring)
 {
     {
-        FlyString a("foo");
-        FlyString b("foo");
+        DeprecatedFlyString a("foo");
+        DeprecatedFlyString b("foo");
         EXPECT_EQ(a.impl(), b.impl());
     }
 
     {
         DeprecatedString a = "foo";
-        FlyString b = a;
+        DeprecatedFlyString b = a;
         StringBuilder builder;
         builder.append('f');
         builder.append("oo"sv);
-        FlyString c = builder.to_deprecated_string();
+        DeprecatedFlyString c = builder.to_deprecated_string();
         EXPECT_EQ(a.impl(), b.impl());
         EXPECT_EQ(a.impl(), c.impl());
     }
diff --git a/Userland/DevTools/Profiler/Profile.cpp b/Userland/DevTools/Profiler/Profile.cpp
index d7f4418b9e9..d590b727874 100644
--- a/Userland/DevTools/Profiler/Profile.cpp
+++ b/Userland/DevTools/Profiler/Profile.cpp
@@ -410,7 +410,7 @@ ErrorOr<NonnullOwnPtr<Profile>> Profile::load_from_perfcore_file(StringView path
             auto const& frame = stack_array.at(i);
             auto ptr = frame.to_number<u64>();
             u32 offset = 0;
-            FlyString object_name;
+            DeprecatedFlyString object_name;
             DeprecatedString symbol;
 
             if (maybe_kernel_base.has_value() && ptr >= maybe_kernel_base.value()) {
@@ -610,7 +610,7 @@ ProfileNode::ProfileNode(Process const& process)
 {
 }
 
-ProfileNode::ProfileNode(Process const& process, FlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
+ProfileNode::ProfileNode(Process const& process, DeprecatedFlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
     : m_process(process)
     , m_symbol(move(symbol))
     , m_pid(pid)
diff --git a/Userland/DevTools/Profiler/Profile.h b/Userland/DevTools/Profiler/Profile.h
index 5c89d88fe15..c8c4d24d915 100644
--- a/Userland/DevTools/Profiler/Profile.h
+++ b/Userland/DevTools/Profiler/Profile.h
@@ -15,7 +15,7 @@
 #include "SignpostsModel.h"
 #include "SourceModel.h"
 #include <AK/Bitmap.h>
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/JsonArray.h>
 #include <AK/JsonObject.h>
 #include <AK/JsonValue.h>
@@ -34,7 +34,7 @@ extern OwnPtr<Debug::DebugInfo> g_kernel_debug_info;
 
 class ProfileNode : public RefCounted<ProfileNode> {
 public:
-    static NonnullRefPtr<ProfileNode> create(Process const& process, FlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
+    static NonnullRefPtr<ProfileNode> create(Process const& process, DeprecatedFlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
     {
         return adopt_ref(*new ProfileNode(process, object_name, move(symbol), address, offset, timestamp, pid));
     }
@@ -53,7 +53,7 @@ public:
     bool has_seen_event(size_t event_index) const { return m_seen_events.get(event_index); }
     void did_see_event(size_t event_index) { m_seen_events.set(event_index, true); }
 
-    FlyString const& object_name() const { return m_object_name; }
+    DeprecatedFlyString const& object_name() const { return m_object_name; }
     DeprecatedString const& symbol() const { return m_symbol; }
     FlatPtr address() const { return m_address; }
     u32 offset() const { return m_offset; }
@@ -74,7 +74,7 @@ public:
         m_children.append(child);
     }
 
-    ProfileNode& find_or_create_child(FlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
+    ProfileNode& find_or_create_child(DeprecatedFlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t pid)
     {
         for (size_t i = 0; i < m_children.size(); ++i) {
             auto& child = m_children[i];
@@ -112,12 +112,12 @@ public:
 
 private:
     explicit ProfileNode(Process const&);
-    explicit ProfileNode(Process const&, FlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t);
+    explicit ProfileNode(Process const&, DeprecatedFlyString const& object_name, DeprecatedString symbol, FlatPtr address, u32 offset, u64 timestamp, pid_t);
 
     bool m_root { false };
     Process const& m_process;
     ProfileNode* m_parent { nullptr };
-    FlyString m_object_name;
+    DeprecatedFlyString m_object_name;
     DeprecatedString m_symbol;
     pid_t m_pid { 0 };
     FlatPtr m_address { 0 };
@@ -166,7 +166,7 @@ public:
     Vector<NonnullRefPtr<ProfileNode>> const& roots() const { return m_roots; }
 
     struct Frame {
-        FlyString object_name;
+        DeprecatedFlyString object_name;
         DeprecatedString symbol;
         FlatPtr address { 0 };
         u32 offset { 0 };
diff --git a/Userland/Libraries/LibAudio/FlacLoader.cpp b/Userland/Libraries/LibAudio/FlacLoader.cpp
index edc9fe77588..2d697a538f2 100644
--- a/Userland/Libraries/LibAudio/FlacLoader.cpp
+++ b/Userland/Libraries/LibAudio/FlacLoader.cpp
@@ -5,9 +5,9 @@
  */
 
 #include <AK/Debug.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
 #include <AK/FixedArray.h>
-#include <AK/FlyString.h>
 #include <AK/Format.h>
 #include <AK/IntegralMath.h>
 #include <AK/Math.h>
diff --git a/Userland/Libraries/LibAudio/LoaderError.h b/Userland/Libraries/LibAudio/LoaderError.h
index 78e47e5e6c4..2464d5cb64c 100644
--- a/Userland/Libraries/LibAudio/LoaderError.h
+++ b/Userland/Libraries/LibAudio/LoaderError.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Error.h>
-#include <AK/FlyString.h>
 #include <errno.h>
 
 namespace Audio {
@@ -28,20 +28,20 @@ struct LoaderError {
     Category category { Category::Unknown };
     // Binary index: where in the file the error occurred.
     size_t index { 0 };
-    FlyString description { DeprecatedString::empty() };
+    DeprecatedFlyString description { DeprecatedString::empty() };
 
     constexpr LoaderError() = default;
-    LoaderError(Category category, size_t index, FlyString description)
+    LoaderError(Category category, size_t index, DeprecatedFlyString description)
         : category(category)
         , index(index)
         , description(move(description))
     {
     }
-    LoaderError(FlyString description)
+    LoaderError(DeprecatedFlyString description)
         : description(move(description))
     {
     }
-    LoaderError(Category category, FlyString description)
+    LoaderError(Category category, DeprecatedFlyString description)
         : category(category)
         , description(move(description))
     {
diff --git a/Userland/Libraries/LibCpp/AST.h b/Userland/Libraries/LibCpp/AST.h
index 095306e585c..1b997c05310 100644
--- a/Userland/Libraries/LibCpp/AST.h
+++ b/Userland/Libraries/LibCpp/AST.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/NonnullRefPtrVector.h>
 #include <AK/Optional.h>
 #include <AK/RefCounted.h>
@@ -47,7 +47,7 @@ public:
         VERIFY(m_end.has_value());
         return m_end.value();
     }
-    FlyString const& filename() const
+    DeprecatedFlyString const& filename() const
     {
         return m_filename;
     }
@@ -78,7 +78,7 @@ private:
     ASTNode* m_parent { nullptr };
     Optional<Position> m_start;
     Optional<Position> m_end;
-    FlyString m_filename;
+    DeprecatedFlyString m_filename;
 };
 
 class TranslationUnit : public ASTNode {
diff --git a/Userland/Libraries/LibCpp/Preprocessor.h b/Userland/Libraries/LibCpp/Preprocessor.h
index de56ca997d5..eb98146a5a5 100644
--- a/Userland/Libraries/LibCpp/Preprocessor.h
+++ b/Userland/Libraries/LibCpp/Preprocessor.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/Optional.h>
@@ -28,7 +28,7 @@ public:
         DeprecatedString key;
         Vector<DeprecatedString> parameters;
         DeprecatedString value;
-        FlyString filename;
+        DeprecatedFlyString filename;
         size_t line { 0 };
         size_t column { 0 };
     };
diff --git a/Userland/Libraries/LibDebug/DebugInfo.cpp b/Userland/Libraries/LibDebug/DebugInfo.cpp
index 25d976d4175..4df6cb3fb35 100644
--- a/Userland/Libraries/LibDebug/DebugInfo.cpp
+++ b/Userland/Libraries/LibDebug/DebugInfo.cpp
@@ -86,8 +86,8 @@ void DebugInfo::prepare_lines()
         all_lines.extend(unit.line_program().lines());
     });
 
-    HashMap<FlyString, Optional<DeprecatedString>> memoized_full_paths;
-    auto compute_full_path = [&](FlyString const& file_path) -> Optional<DeprecatedString> {
+    HashMap<DeprecatedFlyString, Optional<DeprecatedString>> memoized_full_paths;
+    auto compute_full_path = [&](DeprecatedFlyString const& file_path) -> Optional<DeprecatedString> {
         if (file_path.view().contains("Toolchain/"sv) || file_path.view().contains("libgcc"sv))
             return {};
         if (file_path.view().starts_with("./"sv) && !m_source_root.is_null())
diff --git a/Userland/Libraries/LibDebug/DebugInfo.h b/Userland/Libraries/LibDebug/DebugInfo.h
index b73c272ca95..7bb8ff1de50 100644
--- a/Userland/Libraries/LibDebug/DebugInfo.h
+++ b/Userland/Libraries/LibDebug/DebugInfo.h
@@ -29,7 +29,7 @@ public:
     ELF::Image const& elf() const { return m_elf; }
 
     struct SourcePosition {
-        FlyString file_path;
+        DeprecatedFlyString file_path;
         size_t line_number { 0 };
         Optional<FlatPtr> address_of_first_statement;
 
diff --git a/Userland/Libraries/LibDebug/Dwarf/LineProgram.cpp b/Userland/Libraries/LibDebug/Dwarf/LineProgram.cpp
index b1d4bfb4a1f..55d339100da 100644
--- a/Userland/Libraries/LibDebug/Dwarf/LineProgram.cpp
+++ b/Userland/Libraries/LibDebug/Dwarf/LineProgram.cpp
@@ -138,7 +138,7 @@ void LineProgram::append_to_line_info()
     full_path.append('/');
     full_path.append(m_source_files[m_file_index].name);
 
-    m_lines.append({ m_address, FlyString { full_path.string_view() }, m_line });
+    m_lines.append({ m_address, DeprecatedFlyString { full_path.string_view() }, m_line });
 }
 
 void LineProgram::reset_registers()
diff --git a/Userland/Libraries/LibDebug/Dwarf/LineProgram.h b/Userland/Libraries/LibDebug/Dwarf/LineProgram.h
index f09727c0058..089a9098956 100644
--- a/Userland/Libraries/LibDebug/Dwarf/LineProgram.h
+++ b/Userland/Libraries/LibDebug/Dwarf/LineProgram.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/MemoryStream.h>
 #include <AK/Vector.h>
 #include <LibDebug/Dwarf/DwarfTypes.h>
@@ -112,20 +112,20 @@ public:
 
     struct LineInfo {
         FlatPtr address { 0 };
-        FlyString file;
+        DeprecatedFlyString file;
         size_t line { 0 };
     };
 
     Vector<LineInfo> const& lines() const { return m_lines; }
 
     struct DirectoryAndFile {
-        FlyString directory;
-        FlyString filename;
+        DeprecatedFlyString directory;
+        DeprecatedFlyString filename;
     };
     DirectoryAndFile get_directory_and_file(size_t file_index) const;
 
     struct FileEntry {
-        FlyString name;
+        DeprecatedFlyString name;
         size_t directory_index { 0 };
     };
     Vector<FileEntry> const& source_files() const { return m_source_files; }
diff --git a/Userland/Libraries/LibGfx/Font/FontDatabase.cpp b/Userland/Libraries/LibGfx/Font/FontDatabase.cpp
index 42c66122fcf..d9e5d058c16 100644
--- a/Userland/Libraries/LibGfx/Font/FontDatabase.cpp
+++ b/Userland/Libraries/LibGfx/Font/FontDatabase.cpp
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/NonnullRefPtrVector.h>
 #include <AK/Queue.h>
 #include <AK/QuickSort.h>
@@ -118,7 +118,7 @@ Font& FontDatabase::default_fixed_width_font()
 
 struct FontDatabase::Private {
     HashMap<DeprecatedString, NonnullRefPtr<Gfx::Font>> full_name_to_font_map;
-    HashMap<FlyString, Vector<NonnullRefPtr<Typeface>>> typefaces;
+    HashMap<DeprecatedFlyString, Vector<NonnullRefPtr<Typeface>>> typefaces;
 };
 
 void FontDatabase::load_all_fonts_from_path(DeprecatedString const& root)
@@ -214,7 +214,7 @@ RefPtr<Gfx::Font> FontDatabase::get_by_name(StringView name)
     return it->value;
 }
 
-RefPtr<Gfx::Font> FontDatabase::get(FlyString const& family, float point_size, unsigned weight, unsigned slope, Font::AllowInexactSizeMatch allow_inexact_size_match)
+RefPtr<Gfx::Font> FontDatabase::get(DeprecatedFlyString const& family, float point_size, unsigned weight, unsigned slope, Font::AllowInexactSizeMatch allow_inexact_size_match)
 {
     auto it = m_private->typefaces.find(family);
     if (it == m_private->typefaces.end())
@@ -226,7 +226,7 @@ RefPtr<Gfx::Font> FontDatabase::get(FlyString const& family, float point_size, u
     return nullptr;
 }
 
-RefPtr<Gfx::Font> FontDatabase::get(FlyString const& family, FlyString const& variant, float point_size, Font::AllowInexactSizeMatch allow_inexact_size_match)
+RefPtr<Gfx::Font> FontDatabase::get(DeprecatedFlyString const& family, DeprecatedFlyString const& variant, float point_size, Font::AllowInexactSizeMatch allow_inexact_size_match)
 {
     auto it = m_private->typefaces.find(family);
     if (it == m_private->typefaces.end())
diff --git a/Userland/Libraries/LibGfx/Font/FontDatabase.h b/Userland/Libraries/LibGfx/Font/FontDatabase.h
index f46e47b395b..64b9376e532 100644
--- a/Userland/Libraries/LibGfx/Font/FontDatabase.h
+++ b/Userland/Libraries/LibGfx/Font/FontDatabase.h
@@ -48,8 +48,8 @@ public:
     static void set_fixed_width_font_query(DeprecatedString);
     static void set_default_fonts_lookup_path(DeprecatedString);
 
-    RefPtr<Gfx::Font> get(FlyString const& family, float point_size, unsigned weight, unsigned slope, Font::AllowInexactSizeMatch = Font::AllowInexactSizeMatch::No);
-    RefPtr<Gfx::Font> get(FlyString const& family, FlyString const& variant, float point_size, Font::AllowInexactSizeMatch = Font::AllowInexactSizeMatch::No);
+    RefPtr<Gfx::Font> get(DeprecatedFlyString const& family, float point_size, unsigned weight, unsigned slope, Font::AllowInexactSizeMatch = Font::AllowInexactSizeMatch::No);
+    RefPtr<Gfx::Font> get(DeprecatedFlyString const& family, DeprecatedFlyString const& variant, float point_size, Font::AllowInexactSizeMatch = Font::AllowInexactSizeMatch::No);
     RefPtr<Gfx::Font> get_by_name(StringView);
     void for_each_font(Function<void(Gfx::Font const&)>);
     void for_each_fixed_width_font(Function<void(Gfx::Font const&)>);
diff --git a/Userland/Libraries/LibGfx/Font/Typeface.h b/Userland/Libraries/LibGfx/Font/Typeface.h
index 0e445bf76d4..67e3d71436e 100644
--- a/Userland/Libraries/LibGfx/Font/Typeface.h
+++ b/Userland/Libraries/LibGfx/Font/Typeface.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Function.h>
 #include <AK/RefCounted.h>
 #include <AK/Vector.h>
@@ -24,8 +24,8 @@ public:
     {
     }
 
-    FlyString const& family() const { return m_family; }
-    FlyString const& variant() const { return m_variant; }
+    DeprecatedFlyString const& family() const { return m_family; }
+    DeprecatedFlyString const& variant() const { return m_variant; }
     unsigned weight() const;
     u8 slope() const;
 
@@ -39,8 +39,8 @@ public:
     RefPtr<Font> get_font(float point_size, Font::AllowInexactSizeMatch = Font::AllowInexactSizeMatch::No) const;
 
 private:
-    FlyString m_family;
-    FlyString m_variant;
+    DeprecatedFlyString m_family;
+    DeprecatedFlyString m_variant;
 
     Vector<RefPtr<BitmapFont>> m_bitmap_fonts;
     RefPtr<VectorFont> m_vector_font;
diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index 551c2e7a9b0..37832debcd8 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -85,7 +85,7 @@ static void print_indent(int indent)
     out("{}", DeprecatedString::repeated(' ', indent * 2));
 }
 
-static void update_function_name(Value value, FlyString const& name)
+static void update_function_name(Value value, DeprecatedFlyString const& name)
 {
     if (!value.is_function())
         return;
@@ -116,7 +116,7 @@ Completion ScopeNode::evaluate_statements(Interpreter& interpreter) const
 
 // 14.13.4 Runtime Semantics: LabelledEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-labelledevaluation
 // BreakableStatement : IterationStatement
-static Completion labelled_evaluation(Interpreter& interpreter, IterationStatement const& statement, Vector<FlyString> const& label_set)
+static Completion labelled_evaluation(Interpreter& interpreter, IterationStatement const& statement, Vector<DeprecatedFlyString> const& label_set)
 {
     // 1. Let stmtResult be Completion(LoopEvaluation of IterationStatement with argument labelSet).
     auto result = statement.loop_evaluation(interpreter, label_set);
@@ -137,7 +137,7 @@ static Completion labelled_evaluation(Interpreter& interpreter, IterationStateme
 
 // 14.13.4 Runtime Semantics: LabelledEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-labelledevaluation
 // BreakableStatement : SwitchStatement
-static Completion labelled_evaluation(Interpreter& interpreter, SwitchStatement const& statement, Vector<FlyString> const&)
+static Completion labelled_evaluation(Interpreter& interpreter, SwitchStatement const& statement, Vector<DeprecatedFlyString> const&)
 {
     // 1. Let stmtResult be the result of evaluating SwitchStatement.
     auto result = statement.execute_impl(interpreter);
@@ -158,7 +158,7 @@ static Completion labelled_evaluation(Interpreter& interpreter, SwitchStatement
 
 // 14.13.4 Runtime Semantics: LabelledEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-labelledevaluation
 // LabelledStatement : LabelIdentifier : LabelledItem
-static Completion labelled_evaluation(Interpreter& interpreter, LabelledStatement const& statement, Vector<FlyString> const& label_set)
+static Completion labelled_evaluation(Interpreter& interpreter, LabelledStatement const& statement, Vector<DeprecatedFlyString> const& label_set)
 {
     auto const& labelled_item = *statement.labelled_item();
 
@@ -167,7 +167,7 @@ static Completion labelled_evaluation(Interpreter& interpreter, LabelledStatemen
 
     // 2. Let newLabelSet be the list-concatenation of labelSet and « label ».
     // Optimization: Avoid vector copy if possible.
-    Optional<Vector<FlyString>> new_label_set;
+    Optional<Vector<DeprecatedFlyString>> new_label_set;
     if (is<IterationStatement>(labelled_item) || is<SwitchStatement>(labelled_item) || is<LabelledStatement>(labelled_item)) {
         new_label_set = label_set;
         new_label_set->append(label);
@@ -298,7 +298,7 @@ Completion FunctionExpression::execute(Interpreter& interpreter) const
 }
 
 // 15.2.5 Runtime Semantics: InstantiateOrdinaryFunctionExpression, https://tc39.es/ecma262/#sec-runtime-semantics-instantiateordinaryfunctionexpression
-Value FunctionExpression::instantiate_ordinary_function_expression(Interpreter& interpreter, FlyString given_name) const
+Value FunctionExpression::instantiate_ordinary_function_expression(Interpreter& interpreter, DeprecatedFlyString given_name) const
 {
     auto& vm = interpreter.vm();
     auto& realm = *vm.current_realm();
@@ -637,7 +637,7 @@ Completion WithStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.1.1 LoopContinues ( completion, labelSet ), https://tc39.es/ecma262/#sec-loopcontinues
-static bool loop_continues(Completion const& completion, Vector<FlyString> const& label_set)
+static bool loop_continues(Completion const& completion, Vector<DeprecatedFlyString> const& label_set)
 {
     // 1. If completion.[[Type]] is normal, return true.
     if (completion.type() == Completion::Type::Normal)
@@ -669,7 +669,7 @@ Completion WhileStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.3.2 Runtime Semantics: WhileLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-whileloopevaluation
-Completion WhileStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion WhileStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
 
@@ -711,7 +711,7 @@ Completion DoWhileStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.2.2 Runtime Semantics: DoWhileLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-dowhileloopevaluation
-Completion DoWhileStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion DoWhileStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
 
@@ -753,7 +753,7 @@ Completion ForStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.4.2 Runtime Semantics: ForLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forloopevaluation
-Completion ForStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion ForStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
     auto& vm = interpreter.vm();
@@ -1055,7 +1055,7 @@ Completion ForInStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forinofloopevaluation
-Completion ForInStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion ForInStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
     auto& vm = interpreter.vm();
@@ -1121,7 +1121,7 @@ Completion ForOfStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forinofloopevaluation
-Completion ForOfStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion ForOfStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
     auto& vm = interpreter.vm();
@@ -1185,7 +1185,7 @@ Completion ForAwaitOfStatement::execute(Interpreter& interpreter) const
 }
 
 // 14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forinofloopevaluation
-Completion ForAwaitOfStatement::loop_evaluation(Interpreter& interpreter, Vector<FlyString> const& label_set) const
+Completion ForAwaitOfStatement::loop_evaluation(Interpreter& interpreter, Vector<DeprecatedFlyString> const& label_set) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
     auto& vm = interpreter.vm();
@@ -1653,7 +1653,7 @@ ThrowCompletionOr<ClassElement::ClassValue> ClassMethod::class_element_evaluatio
 // 10.2.1.3 Runtime Semantics: EvaluateBody, https://tc39.es/ecma262/#sec-runtime-semantics-evaluatebody
 class ClassFieldInitializerStatement : public Statement {
 public:
-    ClassFieldInitializerStatement(SourceRange source_range, NonnullRefPtr<Expression> expression, FlyString field_name)
+    ClassFieldInitializerStatement(SourceRange source_range, NonnullRefPtr<Expression> expression, DeprecatedFlyString field_name)
         : Statement(source_range)
         , m_expression(move(expression))
         , m_class_field_identifier_name(move(field_name))
@@ -1687,7 +1687,7 @@ public:
 
 private:
     NonnullRefPtr<Expression> m_expression;
-    FlyString m_class_field_identifier_name; // [[ClassFieldIdentifierName]]
+    DeprecatedFlyString m_class_field_identifier_name; // [[ClassFieldIdentifierName]]
 };
 
 // 15.7.10 Runtime Semantics: ClassFieldDefinitionEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-classfielddefinitionevaluation
@@ -1722,19 +1722,19 @@ ThrowCompletionOr<ClassElement::ClassValue> ClassField::class_element_evaluation
     };
 }
 
-static Optional<FlyString> nullopt_or_private_identifier_description(Expression const& expression)
+static Optional<DeprecatedFlyString> nullopt_or_private_identifier_description(Expression const& expression)
 {
     if (is<PrivateIdentifier>(expression))
         return static_cast<PrivateIdentifier const&>(expression).string();
     return {};
 }
 
-Optional<FlyString> ClassField::private_bound_identifier() const
+Optional<DeprecatedFlyString> ClassField::private_bound_identifier() const
 {
     return nullopt_or_private_identifier_description(*m_key);
 }
 
-Optional<FlyString> ClassMethod::private_bound_identifier() const
+Optional<DeprecatedFlyString> ClassMethod::private_bound_identifier() const
 {
     return nullopt_or_private_identifier_description(*m_key);
 }
@@ -1834,7 +1834,7 @@ Completion ClassDeclaration::execute(Interpreter& interpreter) const
 }
 
 // 15.7.14 Runtime Semantics: ClassDefinitionEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-classdefinitionevaluation
-ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_evaluation(Interpreter& interpreter, FlyString const& binding_name, FlyString const& class_name) const
+ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_evaluation(Interpreter& interpreter, DeprecatedFlyString const& binding_name, DeprecatedFlyString const& class_name) const
 {
     auto& vm = interpreter.vm();
     auto& realm = *vm.current_realm();
@@ -2201,7 +2201,7 @@ void ClassDeclaration::dump(int indent) const
     m_class_expression->dump(indent + 1);
 }
 
-ThrowCompletionOr<void> ClassDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> ClassDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     if (m_class_expression->name().is_empty())
         return {};
@@ -2331,7 +2331,7 @@ bool BindingPattern::contains_expression() const
     return false;
 }
 
-ThrowCompletionOr<void> BindingPattern::for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> BindingPattern::for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     for (auto const& entry : entries) {
         auto const& alias = entry.alias;
@@ -2411,7 +2411,7 @@ void FunctionNode::dump(int indent, DeprecatedString const& class_name) const
             if (parameter.is_rest)
                 out("...");
             parameter.binding.visit(
-                [&](FlyString const& name) {
+                [&](DeprecatedFlyString const& name) {
                     outln("{}", name);
                 },
                 [&](BindingPattern const& pattern) {
@@ -2431,7 +2431,7 @@ void FunctionDeclaration::dump(int indent) const
     FunctionNode::dump(indent, class_name());
 }
 
-ThrowCompletionOr<void> FunctionDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> FunctionDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     if (name().is_empty())
         return {};
@@ -2975,7 +2975,7 @@ Completion VariableDeclarator::execute(Interpreter& interpreter) const
     VERIFY_NOT_REACHED();
 }
 
-ThrowCompletionOr<void> VariableDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> VariableDeclaration::for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     for (auto const& entry : declarations()) {
         TRY(entry.target().visit(
@@ -3808,7 +3808,7 @@ void CatchClause::dump(int indent) const
 {
     print_indent(indent);
     m_parameter.visit(
-        [&](FlyString const& parameter) {
+        [&](DeprecatedFlyString const& parameter) {
             if (parameter.is_null())
                 outln("CatchClause");
             else
@@ -3845,7 +3845,7 @@ Completion TryStatement::execute(Interpreter& interpreter) const
         auto catch_environment = new_declarative_environment(*old_environment);
 
         m_handler->parameter().visit(
-            [&](FlyString const& parameter) {
+            [&](DeprecatedFlyString const& parameter) {
                 // 3. For each element argName of the BoundNames of CatchParameter, do
                 // a. Perform ! catchEnv.CreateMutableBinding(argName, false).
                 MUST(catch_environment->create_mutable_binding(vm, parameter, false));
@@ -3863,7 +3863,7 @@ Completion TryStatement::execute(Interpreter& interpreter) const
 
         // 5. Let status be Completion(BindingInitialization of CatchParameter with arguments thrownValue and catchEnv).
         auto status = m_handler->parameter().visit(
-            [&](FlyString const& parameter) {
+            [&](DeprecatedFlyString const& parameter) {
                 return catch_environment->initialize_binding(vm, parameter, thrown_value);
             },
             [&](NonnullRefPtr<BindingPattern> const& pattern) {
@@ -4333,7 +4333,7 @@ ThrowCompletionOr<void> ScopeNode::for_each_lexically_scoped_declaration(ThrowCo
     return {};
 }
 
-ThrowCompletionOr<void> ScopeNode::for_each_lexically_declared_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> ScopeNode::for_each_lexically_declared_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     for (auto const& declaration : m_lexical_declarations) {
         TRY(declaration.for_each_bound_name([&](auto const& name) {
@@ -4343,7 +4343,7 @@ ThrowCompletionOr<void> ScopeNode::for_each_lexically_declared_name(ThrowComplet
     return {};
 }
 
-ThrowCompletionOr<void> ScopeNode::for_each_var_declared_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const
+ThrowCompletionOr<void> ScopeNode::for_each_var_declared_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const
 {
     for (auto& declaration : m_var_declarations) {
         TRY(declaration.for_each_bound_name([&](auto const& name) {
@@ -4407,7 +4407,7 @@ Completion ImportStatement::execute(Interpreter& interpreter) const
     return Optional<Value> {};
 }
 
-FlyString ExportStatement::local_name_for_default = "*default*";
+DeprecatedFlyString ExportStatement::local_name_for_default = "*default*";
 
 // 16.2.3.7 Runtime Semantics: Evaluation, https://tc39.es/ecma262/#sec-exports-runtime-semantics-evaluation
 Completion ExportStatement::execute(Interpreter& interpreter) const
@@ -4557,7 +4557,7 @@ void ImportStatement::dump(int indent) const
     }
 }
 
-bool ExportStatement::has_export(FlyString const& export_name) const
+bool ExportStatement::has_export(DeprecatedFlyString const& export_name) const
 {
     return any_of(m_entries.begin(), m_entries.end(), [&](auto& entry) {
         // Make sure that empty exported names does not overlap with anything
@@ -4567,7 +4567,7 @@ bool ExportStatement::has_export(FlyString const& export_name) const
     });
 }
 
-bool ImportStatement::has_bound_name(FlyString const& name) const
+bool ImportStatement::has_bound_name(DeprecatedFlyString const& name) const
 {
     return any_of(m_entries.begin(), m_entries.end(), [&](auto& entry) {
         return entry.local_name == name;
@@ -4613,7 +4613,7 @@ ThrowCompletionOr<void> Program::global_declaration_instantiation(Interpreter& i
     // 1. Let lexNames be the LexicallyDeclaredNames of script.
     // 2. Let varNames be the VarDeclaredNames of script.
     // 3. For each element name of lexNames, do
-    TRY(for_each_lexically_declared_name([&](FlyString const& name) -> ThrowCompletionOr<void> {
+    TRY(for_each_lexically_declared_name([&](DeprecatedFlyString const& name) -> ThrowCompletionOr<void> {
         // a. If env.HasVarDeclaration(name) is true, throw a SyntaxError exception.
         if (global_environment.has_var_declaration(name))
             return vm.throw_completion<SyntaxError>(ErrorType::TopLevelVariableAlreadyDeclared, name);
@@ -4646,7 +4646,7 @@ ThrowCompletionOr<void> Program::global_declaration_instantiation(Interpreter& i
     Vector<FunctionDeclaration const&> functions_to_initialize;
 
     // 7. Let declaredFunctionNames be a new empty List.
-    HashTable<FlyString> declared_function_names;
+    HashTable<DeprecatedFlyString> declared_function_names;
 
     // 8. For each element d of varDeclarations, in reverse List order, do
 
@@ -4681,7 +4681,7 @@ ThrowCompletionOr<void> Program::global_declaration_instantiation(Interpreter& i
     }));
 
     // 9. Let declaredVarNames be a new empty List.
-    HashTable<FlyString> declared_var_names;
+    HashTable<DeprecatedFlyString> declared_var_names;
 
     // 10. For each element d of varDeclarations, do
     TRY(for_each_var_scoped_variable_declaration([&](Declaration const& declaration) {
@@ -4808,7 +4808,7 @@ ThrowCompletionOr<void> Program::global_declaration_instantiation(Interpreter& i
     return {};
 }
 
-ModuleRequest::ModuleRequest(FlyString module_specifier_, Vector<Assertion> assertions_)
+ModuleRequest::ModuleRequest(DeprecatedFlyString module_specifier_, Vector<Assertion> assertions_)
     : module_specifier(move(module_specifier_))
     , assertions(move(assertions_))
 {
diff --git a/Userland/Libraries/LibJS/AST.h b/Userland/Libraries/LibJS/AST.h
index 8c53cdeff66..8f55a475ccd 100644
--- a/Userland/Libraries/LibJS/AST.h
+++ b/Userland/Libraries/LibJS/AST.h
@@ -8,8 +8,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashMap.h>
 #include <AK/NonnullRefPtrVector.h>
 #include <AK/OwnPtr.h>
@@ -152,7 +152,7 @@ public:
 // 14.13 Labelled Statements, https://tc39.es/ecma262/#sec-labelled-statements
 class LabelledStatement : public Statement {
 public:
-    LabelledStatement(SourceRange source_range, FlyString label, NonnullRefPtr<Statement> labelled_item)
+    LabelledStatement(SourceRange source_range, DeprecatedFlyString label, NonnullRefPtr<Statement> labelled_item)
         : Statement(source_range)
         , m_label(move(label))
         , m_labelled_item(move(labelled_item))
@@ -162,17 +162,17 @@ public:
     virtual Completion execute(Interpreter&) const override;
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const;
 
-    FlyString const& label() const { return m_label; }
-    FlyString& label() { return m_label; }
+    DeprecatedFlyString const& label() const { return m_label; }
+    DeprecatedFlyString& label() { return m_label; }
     NonnullRefPtr<Statement> const& labelled_item() const { return m_labelled_item; }
     NonnullRefPtr<Statement>& labelled_item() { return m_labelled_item; }
 
 private:
     virtual bool is_labelled_statement() const final { return true; }
 
-    FlyString m_label;
+    DeprecatedFlyString m_label;
     NonnullRefPtr<Statement> m_labelled_item;
 };
 
@@ -180,19 +180,19 @@ class LabelableStatement : public Statement {
 public:
     using Statement::Statement;
 
-    Vector<FlyString> const& labels() const { return m_labels; }
-    virtual void add_label(FlyString string) { m_labels.append(move(string)); }
+    Vector<DeprecatedFlyString> const& labels() const { return m_labels; }
+    virtual void add_label(DeprecatedFlyString string) { m_labels.append(move(string)); }
 
 protected:
-    Vector<FlyString> m_labels;
+    Vector<DeprecatedFlyString> m_labels;
 };
 
 class IterationStatement : public Statement {
 public:
     using Statement::Statement;
 
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const = 0;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const = 0;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const;
 
 private:
     virtual bool is_iteration_statement() const final { return true; }
@@ -305,9 +305,9 @@ public:
     [[nodiscard]] size_t lexical_declaration_count() const { return m_lexical_declarations.size(); }
 
     ThrowCompletionOr<void> for_each_lexically_scoped_declaration(ThrowCompletionOrVoidCallback<Declaration const&>&& callback) const;
-    ThrowCompletionOr<void> for_each_lexically_declared_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const;
+    ThrowCompletionOr<void> for_each_lexically_declared_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const;
 
-    ThrowCompletionOr<void> for_each_var_declared_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const;
+    ThrowCompletionOr<void> for_each_var_declared_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const;
 
     ThrowCompletionOr<void> for_each_var_function_declaration_in_reverse_order(ThrowCompletionOrVoidCallback<FunctionDeclaration const&>&& callback) const;
     ThrowCompletionOr<void> for_each_var_scoped_variable_declaration(ThrowCompletionOrVoidCallback<VariableDeclaration const&>&& callback) const;
@@ -334,11 +334,11 @@ private:
 
 // ImportEntry Record, https://tc39.es/ecma262/#table-importentry-record-fields
 struct ImportEntry {
-    FlyString import_name;       // [[ImportName]] if a String
-    FlyString local_name;        // [[LocalName]]
-    bool is_namespace { false }; // [[ImportName]] if `namespace-object`
+    DeprecatedFlyString import_name; // [[ImportName]] if a String
+    DeprecatedFlyString local_name;  // [[LocalName]]
+    bool is_namespace { false };     // [[ImportName]] if `namespace-object`
 
-    ImportEntry(FlyString import_name_, FlyString local_name_, bool is_namespace_ = false)
+    ImportEntry(DeprecatedFlyString import_name_, DeprecatedFlyString local_name_, bool is_namespace_ = false)
         : import_name(move(import_name_))
         , local_name(move(local_name_))
         , is_namespace(is_namespace_)
@@ -372,7 +372,7 @@ public:
 
     virtual void dump(int indent) const override;
 
-    bool has_bound_name(FlyString const& name) const;
+    bool has_bound_name(DeprecatedFlyString const& name) const;
     Vector<ImportEntry> const& entries() const { return m_entries; }
     ModuleRequest const& module_request() const { return m_module_request; }
     ModuleRequest& module_request() { return m_module_request; }
@@ -395,10 +395,10 @@ struct ExportEntry {
         EmptyNamedExport,
     } kind;
 
-    FlyString export_name;          // [[ExportName]]
-    FlyString local_or_import_name; // Either [[ImportName]] or [[LocalName]]
+    DeprecatedFlyString export_name;          // [[ExportName]]
+    DeprecatedFlyString local_or_import_name; // Either [[ImportName]] or [[LocalName]]
 
-    ExportEntry(Kind export_kind, FlyString export_name_, FlyString local_or_import_name_)
+    ExportEntry(Kind export_kind, DeprecatedFlyString export_name_, DeprecatedFlyString local_or_import_name_)
         : kind(export_kind)
         , export_name(move(export_name_))
         , local_or_import_name(move(local_or_import_name_))
@@ -410,7 +410,7 @@ struct ExportEntry {
         return m_module_request != nullptr;
     }
 
-    static ExportEntry indirect_export_entry(ModuleRequest const& module_request, FlyString export_name, FlyString import_name)
+    static ExportEntry indirect_export_entry(ModuleRequest const& module_request, DeprecatedFlyString export_name, DeprecatedFlyString import_name)
     {
         ExportEntry entry { Kind::NamedExport, move(export_name), move(import_name) };
         entry.m_module_request = &module_request;
@@ -428,7 +428,7 @@ private:
     friend class ExportStatement;
 
 public:
-    static ExportEntry named_export(FlyString export_name, FlyString local_name)
+    static ExportEntry named_export(DeprecatedFlyString export_name, DeprecatedFlyString local_name)
     {
         return ExportEntry { Kind::NamedExport, move(export_name), move(local_name) };
     }
@@ -438,7 +438,7 @@ public:
         return ExportEntry { Kind::ModuleRequestAllButDefault, {}, {} };
     }
 
-    static ExportEntry all_module_request(FlyString export_name)
+    static ExportEntry all_module_request(DeprecatedFlyString export_name)
     {
         return ExportEntry { Kind::ModuleRequestAll, move(export_name), {} };
     }
@@ -451,7 +451,7 @@ public:
 
 class ExportStatement final : public Statement {
 public:
-    static FlyString local_name_for_default;
+    static DeprecatedFlyString local_name_for_default;
 
     ExportStatement(SourceRange source_range, RefPtr<ASTNode> statement, Vector<ExportEntry> entries, bool is_default_export, ModuleRequest module_request)
         : Statement(source_range)
@@ -470,7 +470,7 @@ public:
 
     virtual void dump(int indent) const override;
 
-    bool has_export(FlyString const& export_name) const;
+    bool has_export(DeprecatedFlyString const& export_name) const;
 
     bool has_statement() const { return m_statement; }
     Vector<ExportEntry> const& entries() const { return m_entries; }
@@ -592,7 +592,7 @@ public:
     {
     }
 
-    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const = 0;
+    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const = 0;
 
     // 8.1.3 Static Semantics: IsConstantDeclaration, https://tc39.es/ecma262/#sec-static-semantics-isconstantdeclaration
     virtual bool is_constant_declaration() const { return false; }
@@ -608,7 +608,7 @@ public:
     }
     Completion execute(Interpreter&) const override { return {}; }
 
-    ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&&) const override
+    ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&&) const override
     {
         VERIFY_NOT_REACHED();
     }
@@ -633,7 +633,7 @@ struct BindingPattern : RefCounted<BindingPattern> {
 
     void dump(int indent) const;
 
-    ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const;
+    ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const;
 
     bool contains_expression() const;
 
@@ -642,14 +642,14 @@ struct BindingPattern : RefCounted<BindingPattern> {
 };
 
 struct FunctionParameter {
-    Variant<FlyString, NonnullRefPtr<BindingPattern>> binding;
+    Variant<DeprecatedFlyString, NonnullRefPtr<BindingPattern>> binding;
     RefPtr<Expression> default_value;
     bool is_rest { false };
 };
 
 class FunctionNode {
 public:
-    FlyString const& name() const { return m_name; }
+    DeprecatedFlyString const& name() const { return m_name; }
     DeprecatedString const& source_text() const { return m_source_text; }
     Statement const& body() const { return *m_body; }
     Vector<FunctionParameter> const& parameters() const { return m_parameters; };
@@ -661,7 +661,7 @@ public:
     FunctionKind kind() const { return m_kind; }
 
 protected:
-    FunctionNode(FlyString name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function)
+    FunctionNode(DeprecatedFlyString name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function)
         : m_name(move(name))
         , m_source_text(move(source_text))
         , m_body(move(body))
@@ -680,7 +680,7 @@ protected:
     void dump(int indent, DeprecatedString const& class_name) const;
 
 private:
-    FlyString m_name;
+    DeprecatedFlyString m_name;
     DeprecatedString m_source_text;
     NonnullRefPtr<Statement> m_body;
     Vector<FunctionParameter> const m_parameters;
@@ -698,7 +698,7 @@ class FunctionDeclaration final
 public:
     static bool must_have_name() { return true; }
 
-    FunctionDeclaration(SourceRange source_range, FlyString const& name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval)
+    FunctionDeclaration(SourceRange source_range, DeprecatedFlyString const& name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval)
         : Declaration(source_range)
         , FunctionNode(name, move(source_text), move(body), move(parameters), function_length, kind, is_strict_mode, might_need_arguments_object, contains_direct_call_to_eval, false)
     {
@@ -708,7 +708,7 @@ public:
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
 
-    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const override;
+    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const override;
 
     virtual bool is_function_declaration() const override { return true; }
 
@@ -724,7 +724,7 @@ class FunctionExpression final
 public:
     static bool must_have_name() { return false; }
 
-    FunctionExpression(SourceRange source_range, FlyString const& name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function = false)
+    FunctionExpression(SourceRange source_range, DeprecatedFlyString const& name, DeprecatedString source_text, NonnullRefPtr<Statement> body, Vector<FunctionParameter> parameters, i32 function_length, FunctionKind kind, bool is_strict_mode, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function = false)
         : Expression(source_range)
         , FunctionNode(name, move(source_text), move(body), move(parameters), function_length, kind, is_strict_mode, might_need_arguments_object, contains_direct_call_to_eval, is_arrow_function)
     {
@@ -737,7 +737,7 @@ public:
 
     bool has_name() const { return !name().is_empty(); }
 
-    Value instantiate_ordinary_function_expression(Interpreter&, FlyString given_name) const;
+    Value instantiate_ordinary_function_expression(Interpreter&, DeprecatedFlyString given_name) const;
 
 private:
     virtual bool is_function_expression() const override { return true; }
@@ -845,10 +845,10 @@ public:
     Statement const& body() const { return *m_body; }
 
     virtual Completion execute(Interpreter&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const override;
 
 private:
     NonnullRefPtr<Expression> m_test;
@@ -868,10 +868,10 @@ public:
     Statement const& body() const { return *m_body; }
 
     virtual Completion execute(Interpreter&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const override;
 
 private:
     NonnullRefPtr<Expression> m_test;
@@ -916,10 +916,10 @@ public:
     Statement const& body() const { return *m_body; }
 
     virtual Completion execute(Interpreter&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const override;
 
 private:
     RefPtr<ASTNode> m_init;
@@ -944,8 +944,8 @@ public:
 
     virtual Completion execute(Interpreter&) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
 
 private:
@@ -970,8 +970,8 @@ public:
 
     virtual Completion execute(Interpreter&) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
 
 private:
@@ -991,7 +991,7 @@ public:
     }
 
     virtual Completion execute(Interpreter&) const override;
-    virtual Completion loop_evaluation(Interpreter&, Vector<FlyString> const&) const override;
+    virtual Completion loop_evaluation(Interpreter&, Vector<DeprecatedFlyString> const&) const override;
     virtual void dump(int indent) const override;
 
 private:
@@ -1236,13 +1236,13 @@ private:
 
 class Identifier final : public Expression {
 public:
-    explicit Identifier(SourceRange source_range, FlyString string)
+    explicit Identifier(SourceRange source_range, DeprecatedFlyString string)
         : Expression(source_range)
         , m_string(move(string))
     {
     }
 
-    FlyString const& string() const { return m_string; }
+    DeprecatedFlyString const& string() const { return m_string; }
 
     virtual Completion execute(Interpreter&) const override;
     virtual void dump(int indent) const override;
@@ -1252,19 +1252,19 @@ public:
 private:
     virtual bool is_identifier() const override { return true; }
 
-    FlyString m_string;
+    DeprecatedFlyString m_string;
     mutable EnvironmentCoordinate m_cached_environment_coordinate;
 };
 
 class PrivateIdentifier final : public Expression {
 public:
-    explicit PrivateIdentifier(SourceRange source_range, FlyString string)
+    explicit PrivateIdentifier(SourceRange source_range, DeprecatedFlyString string)
         : Expression(source_range)
         , m_string(move(string))
     {
     }
 
-    FlyString const& string() const { return m_string; }
+    DeprecatedFlyString const& string() const { return m_string; }
 
     virtual Completion execute(Interpreter&) const override;
     virtual void dump(int indent) const override;
@@ -1272,7 +1272,7 @@ public:
     virtual bool is_private_identifier() const override { return true; }
 
 private:
-    FlyString m_string;
+    DeprecatedFlyString m_string;
 };
 
 class ClassElement : public ASTNode {
@@ -1298,7 +1298,7 @@ public:
     using ClassValue = Variant<ClassFieldDefinition, Completion, PrivateElement>;
     virtual ThrowCompletionOr<ClassValue> class_element_evaluation(Interpreter&, Object& home_object) const = 0;
 
-    virtual Optional<FlyString> private_bound_identifier() const { return {}; };
+    virtual Optional<DeprecatedFlyString> private_bound_identifier() const { return {}; };
 
 private:
     bool m_is_static { false };
@@ -1326,7 +1326,7 @@ public:
 
     virtual void dump(int indent) const override;
     virtual ThrowCompletionOr<ClassValue> class_element_evaluation(Interpreter&, Object& home_object) const override;
-    virtual Optional<FlyString> private_bound_identifier() const override;
+    virtual Optional<DeprecatedFlyString> private_bound_identifier() const override;
 
 private:
     virtual bool is_class_method() const override { return true; }
@@ -1353,7 +1353,7 @@ public:
 
     virtual void dump(int indent) const override;
     virtual ThrowCompletionOr<ClassValue> class_element_evaluation(Interpreter&, Object& home_object) const override;
-    virtual Optional<FlyString> private_bound_identifier() const override;
+    virtual Optional<DeprecatedFlyString> private_bound_identifier() const override;
 
 private:
     NonnullRefPtr<Expression> m_key;
@@ -1415,7 +1415,7 @@ public:
 
     bool has_name() const { return !m_name.is_empty(); }
 
-    ThrowCompletionOr<ECMAScriptFunctionObject*> class_definition_evaluation(Interpreter&, FlyString const& binding_name = {}, FlyString const& class_name = {}) const;
+    ThrowCompletionOr<ECMAScriptFunctionObject*> class_definition_evaluation(Interpreter&, DeprecatedFlyString const& binding_name = {}, DeprecatedFlyString const& class_name = {}) const;
 
 private:
     virtual bool is_class_expression() const override { return true; }
@@ -1439,7 +1439,7 @@ public:
     virtual void dump(int indent) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
 
-    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const override;
+    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const override;
 
     virtual bool is_lexical_declaration() const override { return true; }
 
@@ -1706,7 +1706,7 @@ public:
 
     NonnullRefPtrVector<VariableDeclarator> const& declarations() const { return m_declarations; }
 
-    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<FlyString const&>&& callback) const override;
+    virtual ThrowCompletionOr<void> for_each_bound_name(ThrowCompletionOrVoidCallback<DeprecatedFlyString const&>&& callback) const override;
 
     virtual bool is_constant_declaration() const override { return m_declaration_kind == DeclarationKind::Const; };
 
@@ -1985,7 +1985,7 @@ private:
 
 class CatchClause final : public ASTNode {
 public:
-    CatchClause(SourceRange source_range, FlyString parameter, NonnullRefPtr<BlockStatement> body)
+    CatchClause(SourceRange source_range, DeprecatedFlyString parameter, NonnullRefPtr<BlockStatement> body)
         : ASTNode(source_range)
         , m_parameter(move(parameter))
         , m_body(move(body))
@@ -2006,7 +2006,7 @@ public:
     virtual Completion execute(Interpreter&) const override;
 
 private:
-    Variant<FlyString, NonnullRefPtr<BindingPattern>> m_parameter;
+    Variant<DeprecatedFlyString, NonnullRefPtr<BindingPattern>> m_parameter;
     NonnullRefPtr<BlockStatement> m_body;
 };
 
@@ -2080,7 +2080,7 @@ public:
     virtual void dump(int indent) const override;
     virtual Completion execute(Interpreter&) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
-    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const;
+    virtual Bytecode::CodeGenerationErrorOr<void> generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const;
 
     Completion execute_impl(Interpreter&) const;
     void add_case(NonnullRefPtr<SwitchCase> switch_case) { m_cases.append(move(switch_case)); }
@@ -2092,7 +2092,7 @@ private:
 
 class BreakStatement final : public Statement {
 public:
-    BreakStatement(SourceRange source_range, FlyString target_label)
+    BreakStatement(SourceRange source_range, DeprecatedFlyString target_label)
         : Statement(source_range)
         , m_target_label(move(target_label))
     {
@@ -2100,16 +2100,16 @@ public:
 
     virtual Completion execute(Interpreter&) const override;
 
-    FlyString const& target_label() const { return m_target_label; }
+    DeprecatedFlyString const& target_label() const { return m_target_label; }
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
 
 private:
-    FlyString m_target_label;
+    DeprecatedFlyString m_target_label;
 };
 
 class ContinueStatement final : public Statement {
 public:
-    ContinueStatement(SourceRange source_range, FlyString target_label)
+    ContinueStatement(SourceRange source_range, DeprecatedFlyString target_label)
         : Statement(source_range)
         , m_target_label(move(target_label))
     {
@@ -2118,10 +2118,10 @@ public:
     virtual Completion execute(Interpreter&) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
 
-    FlyString const& target_label() const { return m_target_label; }
+    DeprecatedFlyString const& target_label() const { return m_target_label; }
 
 private:
-    FlyString m_target_label;
+    DeprecatedFlyString m_target_label;
 };
 
 class DebuggerStatement final : public Statement {
diff --git a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
index 18596af3ea0..e338a2031e8 100644
--- a/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp
@@ -109,7 +109,7 @@ Bytecode::CodeGenerationErrorOr<void> ScopeNode::generate_bytecode(Bytecode::Gen
         Vector<FunctionDeclaration const&> functions_to_initialize;
 
         // 7. Let declaredFunctionNames be a new empty List.
-        HashTable<FlyString> declared_function_names;
+        HashTable<DeprecatedFlyString> declared_function_names;
 
         // 8. For each element d of varDeclarations, in reverse List order, do
         (void)for_each_var_function_declaration_in_reverse_order([&](FunctionDeclaration const& function) -> ThrowCompletionOr<void> {
@@ -135,7 +135,7 @@ Bytecode::CodeGenerationErrorOr<void> ScopeNode::generate_bytecode(Bytecode::Gen
         });
 
         // 9. Let declaredVarNames be a new empty List.
-        HashTable<FlyString> declared_var_names;
+        HashTable<DeprecatedFlyString> declared_var_names;
 
         // 10. For each element d of varDeclarations, do
         (void)for_each_var_scoped_variable_declaration([&](Declaration const& declaration) {
@@ -803,7 +803,7 @@ Bytecode::CodeGenerationErrorOr<void> LabelledStatement::generate_bytecode(Bytec
 
 // 14.13.4 Runtime Semantics: LabelledEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-labelledevaluation
 // LabelledStatement : LabelIdentifier : LabelledItem
-Bytecode::CodeGenerationErrorOr<void> LabelledStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> LabelledStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     // Convert the m_labelled_item NNRP to a reference early so we don't have to do it every single time we want to use it.
     auto const& labelled_item = *m_labelled_item;
@@ -853,7 +853,7 @@ Bytecode::CodeGenerationErrorOr<void> LabelledStatement::generate_labelled_evalu
     return {};
 }
 
-Bytecode::CodeGenerationErrorOr<void> IterationStatement::generate_labelled_evaluation(Bytecode::Generator&, Vector<FlyString> const&) const
+Bytecode::CodeGenerationErrorOr<void> IterationStatement::generate_labelled_evaluation(Bytecode::Generator&, Vector<DeprecatedFlyString> const&) const
 {
     return Bytecode::CodeGenerationError {
         this,
@@ -866,7 +866,7 @@ Bytecode::CodeGenerationErrorOr<void> WhileStatement::generate_bytecode(Bytecode
     return generate_labelled_evaluation(generator, {});
 }
 
-Bytecode::CodeGenerationErrorOr<void> WhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> WhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     // test
     // jump if_false (true) end (false) body
@@ -916,7 +916,7 @@ Bytecode::CodeGenerationErrorOr<void> DoWhileStatement::generate_bytecode(Byteco
     return generate_labelled_evaluation(generator, {});
 }
 
-Bytecode::CodeGenerationErrorOr<void> DoWhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> DoWhileStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     // jump always (true) body
     // test
@@ -967,7 +967,7 @@ Bytecode::CodeGenerationErrorOr<void> ForStatement::generate_bytecode(Bytecode::
     return generate_labelled_evaluation(generator, {});
 }
 
-Bytecode::CodeGenerationErrorOr<void> ForStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> ForStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     // init
     // jump always (true) test
@@ -2215,7 +2215,7 @@ Bytecode::CodeGenerationErrorOr<void> TryStatement::generate_bytecode(Bytecode::
 
         generator.begin_variable_scope(Bytecode::Generator::BindingMode::Lexical, Bytecode::Generator::SurroundingScopeKind::Block);
         TRY(m_handler->parameter().visit(
-            [&](FlyString const& parameter) -> Bytecode::CodeGenerationErrorOr<void> {
+            [&](DeprecatedFlyString const& parameter) -> Bytecode::CodeGenerationErrorOr<void> {
                 if (!parameter.is_empty()) {
                     auto parameter_identifier = generator.intern_identifier(parameter);
                     generator.register_binding(parameter_identifier);
@@ -2283,7 +2283,7 @@ Bytecode::CodeGenerationErrorOr<void> SwitchStatement::generate_bytecode(Bytecod
     return generate_labelled_evaluation(generator, {});
 }
 
-Bytecode::CodeGenerationErrorOr<void> SwitchStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> SwitchStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     auto discriminant_reg = generator.allocate_register();
     TRY(m_discriminant->generate_bytecode(generator));
@@ -2516,7 +2516,7 @@ static Bytecode::CodeGenerationErrorOr<ForInOfHeadEvaluationResult> for_in_of_he
 }
 
 // 14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] ), https://tc39.es/ecma262/#sec-runtime-semantics-forin-div-ofbodyevaluation-lhs-stmt-iterator-lhskind-labelset
-static Bytecode::CodeGenerationErrorOr<void> for_in_of_body_evaluation(Bytecode::Generator& generator, ASTNode const& node, Variant<NonnullRefPtr<ASTNode>, NonnullRefPtr<BindingPattern>> const& lhs, ASTNode const& body, ForInOfHeadEvaluationResult const& head_result, Vector<FlyString> const& label_set, Bytecode::BasicBlock& loop_end, Bytecode::BasicBlock& loop_update)
+static Bytecode::CodeGenerationErrorOr<void> for_in_of_body_evaluation(Bytecode::Generator& generator, ASTNode const& node, Variant<NonnullRefPtr<ASTNode>, NonnullRefPtr<BindingPattern>> const& lhs, ASTNode const& body, ForInOfHeadEvaluationResult const& head_result, Vector<DeprecatedFlyString> const& label_set, Bytecode::BasicBlock& loop_end, Bytecode::BasicBlock& loop_update)
 {
     auto iterator_register = generator.allocate_register();
     generator.emit<Bytecode::Op::Store>(iterator_register);
@@ -2719,7 +2719,7 @@ Bytecode::CodeGenerationErrorOr<void> ForInStatement::generate_bytecode(Bytecode
 }
 
 // 14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-forinofloopevaluation
-Bytecode::CodeGenerationErrorOr<void> ForInStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> ForInStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     auto& loop_end = generator.make_block();
     auto& loop_update = generator.make_block();
@@ -2736,7 +2736,7 @@ Bytecode::CodeGenerationErrorOr<void> ForOfStatement::generate_bytecode(Bytecode
     return generate_labelled_evaluation(generator, {});
 }
 
-Bytecode::CodeGenerationErrorOr<void> ForOfStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<FlyString> const& label_set) const
+Bytecode::CodeGenerationErrorOr<void> ForOfStatement::generate_labelled_evaluation(Bytecode::Generator& generator, Vector<DeprecatedFlyString> const& label_set) const
 {
     auto& loop_end = generator.make_block();
     auto& loop_update = generator.make_block();
diff --git a/Userland/Libraries/LibJS/Bytecode/Executable.h b/Userland/Libraries/LibJS/Bytecode/Executable.h
index 8d454047b18..f69ed9bd210 100644
--- a/Userland/Libraries/LibJS/Bytecode/Executable.h
+++ b/Userland/Libraries/LibJS/Bytecode/Executable.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <LibJS/Bytecode/BasicBlock.h>
 #include <LibJS/Bytecode/IdentifierTable.h>
@@ -15,7 +15,7 @@
 namespace JS::Bytecode {
 
 struct Executable {
-    FlyString name;
+    DeprecatedFlyString name;
     NonnullOwnPtrVector<BasicBlock> basic_blocks;
     NonnullOwnPtr<StringTable> string_table;
     NonnullOwnPtr<IdentifierTable> identifier_table;
@@ -23,7 +23,7 @@ struct Executable {
     bool is_strict_mode { false };
 
     DeprecatedString const& get_string(StringTableIndex index) const { return string_table->get(index); }
-    FlyString const& get_identifier(IdentifierTableIndex index) const { return identifier_table->get(index); }
+    DeprecatedFlyString const& get_identifier(IdentifierTableIndex index) const { return identifier_table->get(index); }
 
     void dump() const;
 };
diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.cpp b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
index 555c6751495..8205f1e895d 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.cpp
@@ -113,7 +113,7 @@ void Generator::end_variable_scope()
     }
 }
 
-void Generator::begin_continuable_scope(Label continue_target, Vector<FlyString> const& language_label_set)
+void Generator::begin_continuable_scope(Label continue_target, Vector<DeprecatedFlyString> const& language_label_set)
 {
     m_continuable_scopes.append({ continue_target, language_label_set });
     start_boundary(BlockBoundaryType::Continue);
@@ -130,7 +130,7 @@ Label Generator::nearest_breakable_scope() const
     return m_breakable_scopes.last().bytecode_target;
 }
 
-void Generator::begin_breakable_scope(Label breakable_target, Vector<FlyString> const& language_label_set)
+void Generator::begin_breakable_scope(Label breakable_target, Vector<DeprecatedFlyString> const& language_label_set)
 {
     m_breakable_scopes.append({ breakable_target, language_label_set });
     start_boundary(BlockBoundaryType::Break);
@@ -262,7 +262,7 @@ CodeGenerationErrorOr<void> Generator::emit_delete_reference(JS::ASTNode const&
     return {};
 }
 
-Label Generator::perform_needed_unwinds_for_labelled_break_and_return_target_block(FlyString const& break_label)
+Label Generator::perform_needed_unwinds_for_labelled_break_and_return_target_block(DeprecatedFlyString const& break_label)
 {
     size_t current_boundary = m_boundaries.size();
     for (auto& breakable_scope : m_breakable_scopes.in_reverse()) {
@@ -294,7 +294,7 @@ Label Generator::perform_needed_unwinds_for_labelled_break_and_return_target_blo
     VERIFY_NOT_REACHED();
 }
 
-Label Generator::perform_needed_unwinds_for_labelled_continue_and_return_target_block(FlyString const& continue_label)
+Label Generator::perform_needed_unwinds_for_labelled_continue_and_return_target_block(DeprecatedFlyString const& continue_label)
 {
     size_t current_boundary = m_boundaries.size();
     for (auto& continuable_scope : m_continuable_scopes.in_reverse()) {
diff --git a/Userland/Libraries/LibJS/Bytecode/Generator.h b/Userland/Libraries/LibJS/Bytecode/Generator.h
index a326b473abf..3f966bcb8d8 100644
--- a/Userland/Libraries/LibJS/Bytecode/Generator.h
+++ b/Userland/Libraries/LibJS/Bytecode/Generator.h
@@ -84,9 +84,9 @@ public:
     CodeGenerationErrorOr<void> emit_store_to_reference(JS::ASTNode const&);
     CodeGenerationErrorOr<void> emit_delete_reference(JS::ASTNode const&);
 
-    void begin_continuable_scope(Label continue_target, Vector<FlyString> const& language_label_set);
+    void begin_continuable_scope(Label continue_target, Vector<DeprecatedFlyString> const& language_label_set);
     void end_continuable_scope();
-    void begin_breakable_scope(Label breakable_target, Vector<FlyString> const& language_label_set);
+    void begin_breakable_scope(Label breakable_target, Vector<DeprecatedFlyString> const& language_label_set);
     void end_breakable_scope();
 
     [[nodiscard]] Label nearest_continuable_scope() const;
@@ -117,7 +117,7 @@ public:
         return m_string_table->insert(move(string));
     }
 
-    IdentifierTableIndex intern_identifier(FlyString string)
+    IdentifierTableIndex intern_identifier(DeprecatedFlyString string)
     {
         return m_identifier_table->insert(move(string));
     }
@@ -213,8 +213,8 @@ public:
         }
     }
 
-    Label perform_needed_unwinds_for_labelled_break_and_return_target_block(FlyString const& break_label);
-    Label perform_needed_unwinds_for_labelled_continue_and_return_target_block(FlyString const& continue_label);
+    Label perform_needed_unwinds_for_labelled_break_and_return_target_block(DeprecatedFlyString const& break_label);
+    Label perform_needed_unwinds_for_labelled_continue_and_return_target_block(DeprecatedFlyString const& continue_label);
 
     void start_boundary(BlockBoundaryType type) { m_boundaries.append(type); }
     void end_boundary(BlockBoundaryType type)
@@ -232,7 +232,7 @@ private:
 
     struct LabelableScope {
         Label bytecode_target;
-        Vector<FlyString> language_label_set;
+        Vector<DeprecatedFlyString> language_label_set;
     };
 
     BasicBlock* m_current_basic_block { nullptr };
diff --git a/Userland/Libraries/LibJS/Bytecode/IdentifierTable.cpp b/Userland/Libraries/LibJS/Bytecode/IdentifierTable.cpp
index 72998174381..95fed273a2c 100644
--- a/Userland/Libraries/LibJS/Bytecode/IdentifierTable.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/IdentifierTable.cpp
@@ -8,7 +8,7 @@
 
 namespace JS::Bytecode {
 
-IdentifierTableIndex IdentifierTable::insert(FlyString string)
+IdentifierTableIndex IdentifierTable::insert(DeprecatedFlyString string)
 {
     for (size_t i = 0; i < m_identifiers.size(); i++) {
         if (m_identifiers[i] == string)
@@ -18,7 +18,7 @@ IdentifierTableIndex IdentifierTable::insert(FlyString string)
     return m_identifiers.size() - 1;
 }
 
-FlyString const& IdentifierTable::get(IdentifierTableIndex index) const
+DeprecatedFlyString const& IdentifierTable::get(IdentifierTableIndex index) const
 {
     return m_identifiers[index.value()];
 }
diff --git a/Userland/Libraries/LibJS/Bytecode/IdentifierTable.h b/Userland/Libraries/LibJS/Bytecode/IdentifierTable.h
index ca9dfe49878..b22a8538798 100644
--- a/Userland/Libraries/LibJS/Bytecode/IdentifierTable.h
+++ b/Userland/Libraries/LibJS/Bytecode/IdentifierTable.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DistinctNumeric.h>
-#include <AK/FlyString.h>
 #include <AK/Vector.h>
 
 namespace JS::Bytecode {
@@ -21,13 +21,13 @@ class IdentifierTable {
 public:
     IdentifierTable() = default;
 
-    IdentifierTableIndex insert(FlyString);
-    FlyString const& get(IdentifierTableIndex) const;
+    IdentifierTableIndex insert(DeprecatedFlyString);
+    DeprecatedFlyString const& get(IdentifierTableIndex) const;
     void dump() const;
     bool is_empty() const { return m_identifiers.is_empty(); }
 
 private:
-    Vector<FlyString> m_identifiers;
+    Vector<DeprecatedFlyString> m_identifiers;
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
index 40c9ef80225..abda1f3be21 100644
--- a/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
+++ b/Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
@@ -51,7 +51,7 @@ Interpreter::ValueAndFrame Interpreter::run_and_return_frame(Executable const& e
     if (vm().execution_context_stack().is_empty() || !vm().running_execution_context().lexical_environment) {
         // The "normal" interpreter pushes an execution context without environment so in that case we also want to push one.
         execution_context.this_value = &m_realm.global_object();
-        static FlyString global_execution_context_name = "(*BC* global execution context)";
+        static DeprecatedFlyString global_execution_context_name = "(*BC* global execution context)";
         execution_context.function_name = global_execution_context_name;
         execution_context.lexical_environment = &m_realm.global_environment();
         execution_context.variable_environment = &m_realm.global_environment();
diff --git a/Userland/Libraries/LibJS/Interpreter.h b/Userland/Libraries/LibJS/Interpreter.h
index d84e93ff3be..ab441e4644a 100644
--- a/Userland/Libraries/LibJS/Interpreter.h
+++ b/Userland/Libraries/LibJS/Interpreter.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashMap.h>
 #include <AK/Weakable.h>
 #include <LibJS/Forward.h>
@@ -54,7 +54,7 @@ public:
             nullptr));
 
         // NOTE: These are not in the spec.
-        static FlyString global_execution_context_name = "(global execution context)";
+        static DeprecatedFlyString global_execution_context_name = "(global execution context)";
         interpreter->m_global_execution_context->function_name = global_execution_context_name;
 
         interpreter->m_realm = make_handle(realm);
diff --git a/Userland/Libraries/LibJS/Lexer.cpp b/Userland/Libraries/LibJS/Lexer.cpp
index 3526a779c5a..ee3deb2517d 100644
--- a/Userland/Libraries/LibJS/Lexer.cpp
+++ b/Userland/Libraries/LibJS/Lexer.cpp
@@ -16,7 +16,7 @@
 
 namespace JS {
 
-HashMap<FlyString, TokenType> Lexer::s_keywords;
+HashMap<DeprecatedFlyString, TokenType> Lexer::s_keywords;
 HashMap<DeprecatedString, TokenType> Lexer::s_three_char_tokens;
 HashMap<DeprecatedString, TokenType> Lexer::s_two_char_tokens;
 HashMap<char, TokenType> Lexer::s_single_char_tokens;
@@ -574,7 +574,7 @@ Token Lexer::next()
     // bunch of Invalid* tokens (bad numeric literals, unterminated comments etc.)
     DeprecatedString token_message;
 
-    Optional<FlyString> identifier;
+    Optional<DeprecatedFlyString> identifier;
     size_t identifier_length = 0;
 
     if (m_current_token.type() == TokenType::RegexLiteral && !is_eof() && is_ascii_alpha(m_current_char) && !did_consume_whitespace_or_comments) {
diff --git a/Userland/Libraries/LibJS/Lexer.h b/Userland/Libraries/LibJS/Lexer.h
index 02f010f41cf..889c78a5ffd 100644
--- a/Userland/Libraries/LibJS/Lexer.h
+++ b/Userland/Libraries/LibJS/Lexer.h
@@ -79,7 +79,7 @@ private:
 
     Optional<size_t> m_hit_invalid_unicode;
 
-    static HashMap<FlyString, TokenType> s_keywords;
+    static HashMap<DeprecatedFlyString, TokenType> s_keywords;
     static HashMap<DeprecatedString, TokenType> s_three_char_tokens;
     static HashMap<DeprecatedString, TokenType> s_two_char_tokens;
     static HashMap<char, TokenType> s_single_char_tokens;
@@ -87,7 +87,7 @@ private:
     struct ParsedIdentifiers : public RefCounted<ParsedIdentifiers> {
         // Resolved identifiers must be kept alive for the duration of the parsing stage, otherwise
         // the only references to these strings are deleted by the Token destructor.
-        HashTable<FlyString> identifiers;
+        HashTable<DeprecatedFlyString> identifiers;
     };
 
     RefPtr<ParsedIdentifiers> m_parsed_identifiers;
diff --git a/Userland/Libraries/LibJS/Module.cpp b/Userland/Libraries/LibJS/Module.cpp
index bba073a044c..38ad302488f 100644
--- a/Userland/Libraries/LibJS/Module.cpp
+++ b/Userland/Libraries/LibJS/Module.cpp
@@ -77,7 +77,7 @@ ThrowCompletionOr<Object*> Module::get_module_namespace(VM& vm)
         auto exported_names = TRY(get_exported_names(vm));
 
         // b. Let unambiguousNames be a new empty List.
-        Vector<FlyString> unambiguous_names;
+        Vector<DeprecatedFlyString> unambiguous_names;
 
         // c. For each element name of exportedNames, do
         for (auto& name : exported_names) {
@@ -100,7 +100,7 @@ ThrowCompletionOr<Object*> Module::get_module_namespace(VM& vm)
 }
 
 // 10.4.6.12 ModuleNamespaceCreate ( module, exports ), https://tc39.es/ecma262/#sec-modulenamespacecreate
-Object* Module::module_namespace_create(VM& vm, Vector<FlyString> unambiguous_names)
+Object* Module::module_namespace_create(VM& vm, Vector<DeprecatedFlyString> unambiguous_names)
 {
     auto& realm = this->realm();
 
diff --git a/Userland/Libraries/LibJS/Module.h b/Userland/Libraries/LibJS/Module.h
index 12345118304..21ac8363663 100644
--- a/Userland/Libraries/LibJS/Module.h
+++ b/Userland/Libraries/LibJS/Module.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Heap/GCPtr.h>
 #include <LibJS/Runtime/Environment.h>
 #include <LibJS/Runtime/Realm.h>
@@ -37,7 +37,7 @@ struct ResolvedBinding {
 
     Type type { Null };
     Module* module { nullptr };
-    FlyString export_name;
+    DeprecatedFlyString export_name;
 
     bool is_valid() const
     {
@@ -76,8 +76,8 @@ public:
     virtual ThrowCompletionOr<void> link(VM& vm) = 0;
     virtual ThrowCompletionOr<Promise*> evaluate(VM& vm) = 0;
 
-    virtual ThrowCompletionOr<Vector<FlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set = {}) = 0;
-    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, FlyString const& export_name, Vector<ResolvedBinding> resolve_set = {}) = 0;
+    virtual ThrowCompletionOr<Vector<DeprecatedFlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set = {}) = 0;
+    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, DeprecatedFlyString const& export_name, Vector<ResolvedBinding> resolve_set = {}) = 0;
 
     virtual ThrowCompletionOr<u32> inner_module_linking(VM& vm, Vector<Module*>& stack, u32 index);
     virtual ThrowCompletionOr<u32> inner_module_evaluation(VM& vm, Vector<Module*>& stack, u32 index);
@@ -93,7 +93,7 @@ protected:
     }
 
 private:
-    Object* module_namespace_create(VM& vm, Vector<FlyString> unambiguous_names);
+    Object* module_namespace_create(VM& vm, Vector<DeprecatedFlyString> unambiguous_names);
 
     // These handles are only safe as long as the VM they live in is valid.
     // But evaluated modules SHOULD be stored in the VM so unless you intentionally
diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index d5d311afe28..e8e5f8bf259 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -65,7 +65,7 @@ public:
         scope_pusher.m_function_parameters = parameters;
         for (auto& parameter : parameters) {
             parameter.binding.visit(
-                [&](FlyString const& name) {
+                [&](DeprecatedFlyString const& name) {
                     scope_pusher.m_forbidden_lexical_names.set(name);
                 },
                 [&](NonnullRefPtr<BindingPattern> const& binding_pattern) {
@@ -102,7 +102,7 @@ public:
         return scope_pusher;
     }
 
-    static ScopePusher catch_scope(Parser& parser, RefPtr<BindingPattern> const& pattern, FlyString const& parameter)
+    static ScopePusher catch_scope(Parser& parser, RefPtr<BindingPattern> const& pattern, DeprecatedFlyString const& parameter)
     {
         ScopePusher scope_pusher(parser, nullptr, ScopeLevel::NotTopLevel);
         if (pattern) {
@@ -208,7 +208,7 @@ public:
     ScopePusher* parent_scope() { return m_parent_scope; }
     ScopePusher const* parent_scope() const { return m_parent_scope; }
 
-    [[nodiscard]] bool has_declaration(FlyString const& name) const
+    [[nodiscard]] bool has_declaration(DeprecatedFlyString const& name) const
     {
         return m_lexical_names.contains(name) || m_var_names.contains(name) || !m_functions_to_hoist.find_if([&name](auto& function) { return function->name() == name; }).is_end();
     }
@@ -254,7 +254,7 @@ public:
     }
 
 private:
-    void throw_identifier_declared(FlyString const& name, NonnullRefPtr<Declaration> const& declaration)
+    void throw_identifier_declared(DeprecatedFlyString const& name, NonnullRefPtr<Declaration> const& declaration)
     {
         m_parser.syntax_error(DeprecatedString::formatted("Identifier '{}' already declared", name), declaration->source_range().start);
     }
@@ -266,12 +266,12 @@ private:
     ScopePusher* m_parent_scope { nullptr };
     ScopePusher* m_top_level_scope { nullptr };
 
-    HashTable<FlyString> m_lexical_names;
-    HashTable<FlyString> m_var_names;
-    HashTable<FlyString> m_function_names;
+    HashTable<DeprecatedFlyString> m_lexical_names;
+    HashTable<DeprecatedFlyString> m_var_names;
+    HashTable<DeprecatedFlyString> m_function_names;
 
-    HashTable<FlyString> m_forbidden_lexical_names;
-    HashTable<FlyString> m_forbidden_var_names;
+    HashTable<DeprecatedFlyString> m_forbidden_lexical_names;
+    HashTable<DeprecatedFlyString> m_forbidden_var_names;
     NonnullRefPtrVector<FunctionDeclaration> m_functions_to_hoist;
 
     Optional<Vector<FunctionParameter>> m_function_parameters;
@@ -707,7 +707,7 @@ static bool is_strict_reserved_word(StringView str)
 static bool is_simple_parameter_list(Vector<FunctionParameter> const& parameters)
 {
     return all_of(parameters, [](FunctionParameter const& parameter) {
-        return !parameter.is_rest && parameter.default_value.is_null() && parameter.binding.has<FlyString>();
+        return !parameter.is_rest && parameter.default_value.is_null() && parameter.binding.has<DeprecatedFlyString>();
     });
 }
 
@@ -782,7 +782,7 @@ RefPtr<FunctionExpression> Parser::try_parse_arrow_function_expression(bool expe
             syntax_error("BindingIdentifier may not be 'arguments' or 'eval' in strict mode");
         if (is_async && token.value() == "await"sv)
             syntax_error("'await' is a reserved identifier in async functions");
-        parameters.append({ FlyString { token.value() }, {} });
+        parameters.append({ DeprecatedFlyString { token.value() }, {} });
     }
     // If there's a newline between the closing paren and arrow it's not a valid arrow function,
     // ASI should kick in instead (it'll then fail with "Unexpected token Arrow")
@@ -844,7 +844,7 @@ RefPtr<FunctionExpression> Parser::try_parse_arrow_function_expression(bool expe
     if (body->in_strict_mode()) {
         for (auto& parameter : parameters) {
             parameter.binding.visit(
-                [&](FlyString const& name) {
+                [&](DeprecatedFlyString const& name) {
                     check_identifier_name_for_assignment_validity(name, true);
                 },
                 [&](auto const&) {});
@@ -1046,10 +1046,10 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
     NonnullRefPtrVector<ClassElement> elements;
     RefPtr<Expression> super_class;
     RefPtr<FunctionExpression> constructor;
-    HashTable<FlyString> found_private_names;
+    HashTable<DeprecatedFlyString> found_private_names;
 
-    FlyString class_name = expect_class_name || match_identifier() || match(TokenType::Yield) || match(TokenType::Await)
-        ? consume_identifier_reference().flystring_value()
+    DeprecatedFlyString class_name = expect_class_name || match_identifier() || match(TokenType::Yield) || match(TokenType::Await)
+        ? consume_identifier_reference().DeprecatedFlyString_value()
         : "";
 
     check_identifier_name_for_assignment_validity(class_name, true);
@@ -1331,7 +1331,7 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
             //          this function does not.
             //          So we use a custom version of SuperCall which doesn't use the @@iterator
             //          method on %Array.prototype% visibly.
-            FlyString argument_name = "args";
+            DeprecatedFlyString argument_name = "args";
             auto super_call = create_ast_node<SuperCall>(
                 { m_source_code, rule_start.position(), position() },
                 SuperCall::IsPartOfSyntheticConstructor::Yes,
@@ -1728,7 +1728,7 @@ NonnullRefPtr<ObjectExpression> Parser::parse_object_expression()
                 property_key = parse_property_key();
             } else {
                 property_key = create_ast_node<StringLiteral>({ m_source_code, rule_start.position(), position() }, identifier.value());
-                property_value = create_ast_node<Identifier>({ m_source_code, rule_start.position(), position() }, identifier.flystring_value());
+                property_value = create_ast_node<Identifier>({ m_source_code, rule_start.position(), position() }, identifier.DeprecatedFlyString_value());
             }
         } else {
             property_key = parse_property_key();
@@ -2145,7 +2145,7 @@ Parser::ExpressionResult Parser::parse_secondary_expression(NonnullRefPtr<Expres
             expected("IdentifierName");
         }
 
-        return create_ast_node<MemberExpression>({ m_source_code, rule_start.position(), position() }, move(lhs), create_ast_node<Identifier>({ m_source_code, rule_start.position(), position() }, consume().flystring_value()));
+        return create_ast_node<MemberExpression>({ m_source_code, rule_start.position(), position() }, move(lhs), create_ast_node<Identifier>({ m_source_code, rule_start.position(), position() }, consume().DeprecatedFlyString_value()));
     case TokenType::BracketOpen: {
         consume(TokenType::BracketOpen);
         auto expression = create_ast_node<MemberExpression>({ m_source_code, rule_start.position(), position() }, move(lhs), parse_expression(0), true);
@@ -2322,7 +2322,7 @@ NonnullRefPtr<Identifier> Parser::parse_identifier()
         syntax_error("'arguments' is not allowed in class field initializer");
     return create_ast_node<Identifier>(
         { m_source_code, identifier_start, position() },
-        token.flystring_value());
+        token.DeprecatedFlyString_value());
 }
 
 Vector<CallExpression::Argument> Parser::parse_arguments()
@@ -2501,7 +2501,7 @@ NonnullRefPtr<FunctionBody> Parser::parse_function_body(Vector<FunctionParameter
         Vector<StringView> parameter_names;
         for (auto& parameter : parameters) {
             parameter.binding.visit(
-                [&](FlyString const& parameter_name) {
+                [&](DeprecatedFlyString const& parameter_name) {
                     check_identifier_name_for_assignment_validity(parameter_name, function_body->in_strict_mode());
                     if (function_kind == FunctionKind::Generator && parameter_name == "yield"sv)
                         syntax_error("Parameter name 'yield' not allowed in this context");
@@ -2579,7 +2579,7 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u16 parse_options, O
         function_kind = FunctionKind::Async;
     else
         function_kind = FunctionKind::Normal;
-    FlyString name;
+    DeprecatedFlyString name;
     if (parse_options & FunctionNodeParseOptions::CheckForFunctionAndName) {
         if (function_kind == FunctionKind::Normal && match(TokenType::Async) && !next_token().trivia_contains_line_terminator()) {
             function_kind = FunctionKind::Async;
@@ -2596,9 +2596,9 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u16 parse_options, O
         if (parse_options & FunctionNodeParseOptions::HasDefaultExportName)
             name = ExportStatement::local_name_for_default;
         else if (FunctionNodeType::must_have_name() || match_identifier())
-            name = consume_identifier().flystring_value();
+            name = consume_identifier().DeprecatedFlyString_value();
         else if (is_function_expression && (match(TokenType::Yield) || match(TokenType::Await)))
-            name = consume().flystring_value();
+            name = consume().DeprecatedFlyString_value();
 
         check_identifier_name_for_assignment_validity(name);
 
@@ -2656,18 +2656,18 @@ Vector<FunctionParameter> Parser::parse_formal_parameters(int& function_length,
 
     Vector<FunctionParameter> parameters;
 
-    auto consume_identifier_or_binding_pattern = [&]() -> Variant<FlyString, NonnullRefPtr<BindingPattern>> {
+    auto consume_identifier_or_binding_pattern = [&]() -> Variant<DeprecatedFlyString, NonnullRefPtr<BindingPattern>> {
         if (auto pattern = parse_binding_pattern(AllowDuplicates::No, AllowMemberExpressions::No))
             return pattern.release_nonnull();
 
         auto token = consume_identifier();
-        auto parameter_name = token.flystring_value();
+        auto parameter_name = token.DeprecatedFlyString_value();
 
         check_identifier_name_for_assignment_validity(parameter_name);
 
         for (auto& parameter : parameters) {
             bool has_same_name = parameter.binding.visit(
-                [&](FlyString const& name) {
+                [&](DeprecatedFlyString const& name) {
                     return name == parameter_name;
                 },
                 [&](NonnullRefPtr<BindingPattern> const& bindings) {
@@ -2695,7 +2695,7 @@ Vector<FunctionParameter> Parser::parse_formal_parameters(int& function_length,
                 syntax_error(message, Position { token.line_number(), token.line_column() });
             break;
         }
-        return FlyString { token.value() };
+        return DeprecatedFlyString { token.value() };
     };
 
     while (match(TokenType::CurlyOpen) || match(TokenType::BracketOpen) || match_identifier() || match(TokenType::TripleDot)) {
@@ -2743,7 +2743,7 @@ Vector<FunctionParameter> Parser::parse_formal_parameters(int& function_length,
     return parameters;
 }
 
-static AK::Array<FlyString, 36> s_reserved_words = { "break", "case", "catch", "class", "const", "continue", "debugger", "default", "delete", "do", "else", "enum", "export", "extends", "false", "finally", "for", "function", "if", "import", "in", "instanceof", "new", "null", "return", "super", "switch", "this", "throw", "true", "try", "typeof", "var", "void", "while", "with" };
+static AK::Array<DeprecatedFlyString, 36> s_reserved_words = { "break", "case", "catch", "class", "const", "continue", "debugger", "default", "delete", "do", "else", "enum", "export", "extends", "false", "finally", "for", "function", "if", "import", "in", "instanceof", "new", "null", "return", "super", "switch", "this", "throw", "true", "try", "typeof", "var", "void", "while", "with" };
 
 RefPtr<BindingPattern> Parser::parse_binding_pattern(Parser::AllowDuplicates allow_duplicates, Parser::AllowMemberExpressions allow_member_expressions)
 {
@@ -2806,15 +2806,15 @@ RefPtr<BindingPattern> Parser::parse_binding_pattern(Parser::AllowDuplicates all
                         { m_source_code, rule_start.position(), position() },
                         string_literal->value());
                 } else if (match(TokenType::BigIntLiteral)) {
-                    auto string_value = consume().flystring_value();
+                    auto string_value = consume().DeprecatedFlyString_value();
                     VERIFY(string_value.ends_with("n"sv));
                     name = create_ast_node<Identifier>(
                         { m_source_code, rule_start.position(), position() },
-                        FlyString(string_value.view().substring_view(0, string_value.length() - 1)));
+                        DeprecatedFlyString(string_value.view().substring_view(0, string_value.length() - 1)));
                 } else {
                     name = create_ast_node<Identifier>(
                         { m_source_code, rule_start.position(), position() },
-                        consume().flystring_value());
+                        consume().DeprecatedFlyString_value());
                 }
             } else if (match(TokenType::BracketOpen)) {
                 consume();
@@ -2852,7 +2852,7 @@ RefPtr<BindingPattern> Parser::parse_binding_pattern(Parser::AllowDuplicates all
                 } else if (match_identifier_name()) {
                     alias = create_ast_node<Identifier>(
                         { m_source_code, rule_start.position(), position() },
-                        consume().flystring_value());
+                        consume().DeprecatedFlyString_value());
 
                 } else {
                     expected("identifier or binding pattern");
@@ -2888,7 +2888,7 @@ RefPtr<BindingPattern> Parser::parse_binding_pattern(Parser::AllowDuplicates all
                 alias = pattern.release_nonnull();
             } else if (match_identifier_name()) {
                 // BindingElement must always have an Empty name field
-                auto identifier_name = consume_identifier().flystring_value();
+                auto identifier_name = consume_identifier().DeprecatedFlyString_value();
                 alias = create_ast_node<Identifier>(
                     { m_source_code, rule_start.position(), position() },
                     identifier_name);
@@ -2974,7 +2974,7 @@ NonnullRefPtr<VariableDeclaration> Parser::parse_variable_declaration(bool for_l
         Variant<NonnullRefPtr<Identifier>, NonnullRefPtr<BindingPattern>, Empty> target {};
         if (match_identifier()) {
             auto identifier_start = push_start();
-            auto name = consume_identifier().flystring_value();
+            auto name = consume_identifier().DeprecatedFlyString_value();
             target = create_ast_node<Identifier>(
                 { m_source_code, rule_start.position(), position() },
                 name);
@@ -2996,14 +2996,14 @@ NonnullRefPtr<VariableDeclaration> Parser::parse_variable_declaration(bool for_l
 
             target = create_ast_node<Identifier>(
                 { m_source_code, rule_start.position(), position() },
-                consume().flystring_value());
+                consume().DeprecatedFlyString_value());
         } else if (!m_state.await_expression_is_valid && match(TokenType::Async)) {
             if (m_program_type == Program::Type::Module)
                 syntax_error("Identifier must not be a reserved word in modules ('async')");
 
             target = create_ast_node<Identifier>(
                 { m_source_code, rule_start.position(), position() },
-                consume().flystring_value());
+                consume().DeprecatedFlyString_value());
         }
 
         if (target.has<Empty>()) {
@@ -3070,7 +3070,7 @@ NonnullRefPtr<BreakStatement> Parser::parse_break_statement()
 {
     auto rule_start = push_start();
     consume(TokenType::Break);
-    FlyString target_label;
+    DeprecatedFlyString target_label;
     if (match(TokenType::Semicolon)) {
         consume();
     } else {
@@ -3097,7 +3097,7 @@ NonnullRefPtr<ContinueStatement> Parser::parse_continue_statement()
         syntax_error("'continue' not allow outside of a loop");
 
     consume(TokenType::Continue);
-    FlyString target_label;
+    DeprecatedFlyString target_label;
     if (match(TokenType::Semicolon)) {
         consume();
         return create_ast_node<ContinueStatement>({ m_source_code, rule_start.position(), position() }, target_label);
@@ -3166,7 +3166,7 @@ NonnullRefPtr<OptionalChain> Parser::parse_optional_chain(NonnullRefPtr<Expressi
                     auto start = position();
                     auto identifier = consume();
                     chain.append(OptionalChain::MemberReference {
-                        create_ast_node<Identifier>({ m_source_code, start, position() }, identifier.flystring_value()),
+                        create_ast_node<Identifier>({ m_source_code, start, position() }, identifier.DeprecatedFlyString_value()),
                         OptionalChain::Mode::Optional,
                     });
                 } else {
@@ -3192,7 +3192,7 @@ NonnullRefPtr<OptionalChain> Parser::parse_optional_chain(NonnullRefPtr<Expressi
                 auto start = position();
                 auto identifier = consume();
                 chain.append(OptionalChain::MemberReference {
-                    create_ast_node<Identifier>({ m_source_code, start, position() }, identifier.flystring_value()),
+                    create_ast_node<Identifier>({ m_source_code, start, position() }, identifier.DeprecatedFlyString_value()),
                     OptionalChain::Mode::NotOptional,
                 });
             } else {
@@ -3356,7 +3356,7 @@ NonnullRefPtr<CatchClause> Parser::parse_catch_clause()
     auto rule_start = push_start();
     consume(TokenType::Catch);
 
-    FlyString parameter;
+    DeprecatedFlyString parameter;
     RefPtr<BindingPattern> pattern_parameter;
     auto should_expect_parameter = false;
     if (match(TokenType::ParenOpen)) {
@@ -3375,7 +3375,7 @@ NonnullRefPtr<CatchClause> Parser::parse_catch_clause()
     if (should_expect_parameter && parameter.is_empty() && !pattern_parameter)
         expected("an identifier or a binding pattern");
 
-    HashTable<FlyString> bound_names;
+    HashTable<DeprecatedFlyString> bound_names;
 
     if (pattern_parameter) {
         pattern_parameter->for_each_bound_name(
@@ -3504,7 +3504,7 @@ NonnullRefPtr<Statement> Parser::parse_for_statement()
                 m_state.current_scope_pusher->add_declaration(declaration);
             } else {
                 // This does not follow the normal declaration structure so we need additional checks.
-                HashTable<FlyString> bound_names;
+                HashTable<DeprecatedFlyString> bound_names;
                 declaration->for_each_bound_name([&](auto const& name) {
                     if (bound_names.set(name) != AK::HashSetResult::InsertedNewEntry)
                         syntax_error(DeprecatedString::formatted("Identifier '{}' already declared in for loop initializer", name), declaration->source_range().start);
@@ -4055,7 +4055,7 @@ void Parser::discard_saved_state()
     m_saved_state.take_last();
 }
 
-void Parser::check_identifier_name_for_assignment_validity(FlyString const& name, bool force_strict)
+void Parser::check_identifier_name_for_assignment_validity(DeprecatedFlyString const& name, bool force_strict)
 {
     // FIXME: this is now called from multiple places maybe the error message should be dynamic?
     if (any_of(s_reserved_words, [&](auto& value) { return name == value; })) {
@@ -4073,11 +4073,11 @@ bool Parser::match_assert_clause() const
     return !m_state.current_token.trivia_contains_line_terminator() && m_state.current_token.original_value() == "assert"sv;
 }
 
-FlyString Parser::consume_string_value()
+DeprecatedFlyString Parser::consume_string_value()
 {
     VERIFY(match(TokenType::StringLiteral));
     auto string_token = consume();
-    FlyString value = parse_string_literal(string_token)->value();
+    DeprecatedFlyString value = parse_string_literal(string_token)->value();
 
     // This also checks IsStringWellFormedUnicode which makes sure there is no unpaired surrogate
     // Surrogates are at least 3 bytes
@@ -4148,7 +4148,7 @@ ModuleRequest Parser::parse_module_request()
     return request;
 }
 
-static FlyString default_string_value = "default";
+static DeprecatedFlyString default_string_value = "default";
 
 NonnullRefPtr<ImportStatement> Parser::parse_import_statement(Program& program)
 {
@@ -4237,13 +4237,13 @@ NonnullRefPtr<ImportStatement> Parser::parse_import_statement(Program& program)
                 // ImportSpecifier :  ImportedBinding
                 auto require_as = !match_imported_binding();
                 auto name_position = position();
-                auto name = consume().flystring_value();
+                auto name = consume().DeprecatedFlyString_value();
 
                 if (match_as()) {
                     consume(TokenType::Identifier);
 
                     auto alias_position = position();
-                    auto alias = consume_identifier().flystring_value();
+                    auto alias = consume_identifier().DeprecatedFlyString_value();
                     check_identifier_name_for_assignment_validity(alias);
 
                     entries_with_location.append({ { name, alias }, alias_position });
@@ -4264,7 +4264,7 @@ NonnullRefPtr<ImportStatement> Parser::parse_import_statement(Program& program)
                 consume(TokenType::Identifier);
 
                 auto alias_position = position();
-                auto alias = consume_identifier().flystring_value();
+                auto alias = consume_identifier().DeprecatedFlyString_value();
                 check_identifier_name_for_assignment_validity(alias);
 
                 entries_with_location.append({ { move(name), alias }, alias_position });
@@ -4351,7 +4351,7 @@ NonnullRefPtr<ExportStatement> Parser::parse_export_statement(Program& program)
         auto default_position = position();
         consume(TokenType::Default);
 
-        FlyString local_name;
+        DeprecatedFlyString local_name;
 
         auto lookahead_token = next_token();
 
@@ -4466,7 +4466,7 @@ NonnullRefPtr<ExportStatement> Parser::parse_export_statement(Program& program)
             Required
         } check_for_from { FromSpecifier::NotAllowed };
 
-        auto parse_module_export_name = [&](bool lhs) -> FlyString {
+        auto parse_module_export_name = [&](bool lhs) -> DeprecatedFlyString {
             // https://tc39.es/ecma262/#prod-ModuleExportName
             //  ModuleExportName :
             //      IdentifierName
diff --git a/Userland/Libraries/LibJS/Parser.h b/Userland/Libraries/LibJS/Parser.h
index 7fd192f5e68..e0f399b84d5 100644
--- a/Userland/Libraries/LibJS/Parser.h
+++ b/Userland/Libraries/LibJS/Parser.h
@@ -234,7 +234,7 @@ private:
 
     Token next_token(size_t steps = 1) const;
 
-    void check_identifier_name_for_assignment_validity(FlyString const&, bool force_strict = false);
+    void check_identifier_name_for_assignment_validity(DeprecatedFlyString const&, bool force_strict = false);
 
     bool try_parse_arrow_function_expression_failed_at_position(Position const&) const;
     void set_try_parse_arrow_function_expression_failed_at_position(Position const&, bool);
@@ -244,7 +244,7 @@ private:
     bool parse_directive(ScopeNode& body);
     void parse_statement_list(ScopeNode& output_node, AllowLabelledFunction allow_labelled_functions = AllowLabelledFunction::No);
 
-    FlyString consume_string_value();
+    DeprecatedFlyString consume_string_value();
     ModuleRequest parse_module_request();
 
     struct RulePosition {
@@ -320,7 +320,7 @@ private:
     NonnullRefPtr<SourceCode> m_source_code;
     Vector<Position> m_rule_starts;
     ParserState m_state;
-    FlyString m_filename;
+    DeprecatedFlyString m_filename;
     Vector<ParserState> m_saved_state;
     HashMap<Position, TokenMemoization, PositionKeyTraits> m_token_memoizations;
     Program::Type m_program_type;
diff --git a/Userland/Libraries/LibJS/Print.cpp b/Userland/Libraries/LibJS/Print.cpp
index 0452a201e21..dd1b2bb6f0f 100644
--- a/Userland/Libraries/LibJS/Print.cpp
+++ b/Userland/Libraries/LibJS/Print.cpp
@@ -102,7 +102,7 @@ ErrorOr<void> js_out(JS::PrintContext& print_context, CheckedFormatString<Args..
     return {};
 }
 
-ErrorOr<void> print_type(JS::PrintContext& print_context, FlyString const& name)
+ErrorOr<void> print_type(JS::PrintContext& print_context, DeprecatedFlyString const& name)
 {
     return js_out(print_context, "[\033[36;1m{}\033[0m]", name);
 }
diff --git a/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp b/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
index d1ea5e18b52..9a539019caf 100644
--- a/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
+++ b/Userland/Libraries/LibJS/Runtime/AbstractOperations.cpp
@@ -201,7 +201,7 @@ ThrowCompletionOr<Realm*> get_function_realm(VM& vm, FunctionObject const& funct
 }
 
 // 8.5.2.1 InitializeBoundName ( name, value, environment ), https://tc39.es/ecma262/#sec-initializeboundname
-ThrowCompletionOr<void> initialize_bound_name(VM& vm, FlyString const& name, Value value, Environment* environment)
+ThrowCompletionOr<void> initialize_bound_name(VM& vm, DeprecatedFlyString const& name, Value value, Environment* environment)
 {
     // 1. If environment is not undefined, then
     if (environment) {
@@ -794,7 +794,7 @@ ThrowCompletionOr<void> eval_declaration_instantiation(VM& vm, Program const& pr
     Vector<FunctionDeclaration const&> functions_to_initialize;
 
     // 9. Let declaredFunctionNames be a new empty List.
-    HashTable<FlyString> declared_function_names;
+    HashTable<DeprecatedFlyString> declared_function_names;
 
     // 10. For each element d of varDeclarations, in reverse List order, do
     TRY(program.for_each_var_function_declaration_in_reverse_order([&](FunctionDeclaration const& function) -> ThrowCompletionOr<void> {
@@ -835,7 +835,7 @@ ThrowCompletionOr<void> eval_declaration_instantiation(VM& vm, Program const& pr
     if (!strict) {
         // a. Let declaredFunctionOrVarNames be the list-concatenation of declaredFunctionNames and declaredVarNames.
         // The spec here uses 'declaredVarNames' but that has not been declared yet.
-        HashTable<FlyString> hoisted_functions;
+        HashTable<DeprecatedFlyString> hoisted_functions;
 
         // b. For each FunctionDeclaration f that is directly contained in the StatementList of a Block, CaseClause, or DefaultClause Contained within body, do
         TRY(program.for_each_function_hoistable_with_annexB_extension([&](FunctionDeclaration& function_declaration) -> ThrowCompletionOr<void> {
@@ -926,7 +926,7 @@ ThrowCompletionOr<void> eval_declaration_instantiation(VM& vm, Program const& pr
     }
 
     // 12. Let declaredVarNames be a new empty List.
-    HashTable<FlyString> declared_var_names;
+    HashTable<DeprecatedFlyString> declared_var_names;
 
     // 13. For each element d of varDeclarations, do
     TRY(program.for_each_var_scoped_variable_declaration([&](VariableDeclaration const& declaration) {
@@ -1119,14 +1119,14 @@ Object* create_mapped_arguments_object(VM& vm, FunctionObject& function, Vector<
     MUST(object->define_property_or_throw(vm.names.length, { .value = Value(length), .writable = true, .enumerable = false, .configurable = true }));
 
     // 17. Let mappedNames be a new empty List.
-    HashTable<FlyString> mapped_names;
+    HashTable<DeprecatedFlyString> mapped_names;
 
     // 18. Set index to numberOfParameters - 1.
     // 19. Repeat, while index ≥ 0,
     VERIFY(formals.size() <= NumericLimits<i32>::max());
     for (i32 index = static_cast<i32>(formals.size()) - 1; index >= 0; --index) {
         // a. Let name be parameterNames[index].
-        auto const& name = formals[index].binding.get<FlyString>();
+        auto const& name = formals[index].binding.get<DeprecatedFlyString>();
 
         // b. If name is not an element of mappedNames, then
         if (mapped_names.contains(name))
diff --git a/Userland/Libraries/LibJS/Runtime/AbstractOperations.h b/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
index 4a9ea38d34d..8dd573dc6b8 100644
--- a/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
+++ b/Userland/Libraries/LibJS/Runtime/AbstractOperations.h
@@ -35,7 +35,7 @@ ThrowCompletionOr<size_t> length_of_array_like(VM&, Object const&);
 ThrowCompletionOr<MarkedVector<Value>> create_list_from_array_like(VM&, Value, Function<ThrowCompletionOr<void>(Value)> = {});
 ThrowCompletionOr<FunctionObject*> species_constructor(VM&, Object const&, FunctionObject& default_constructor);
 ThrowCompletionOr<Realm*> get_function_realm(VM&, FunctionObject const&);
-ThrowCompletionOr<void> initialize_bound_name(VM&, FlyString const&, Value, Environment*);
+ThrowCompletionOr<void> initialize_bound_name(VM&, DeprecatedFlyString const&, Value, Environment*);
 bool is_compatible_property_descriptor(bool extensible, PropertyDescriptor const&, Optional<PropertyDescriptor> const& current);
 bool validate_and_apply_property_descriptor(Object*, PropertyKey const&, bool extensible, PropertyDescriptor const&, Optional<PropertyDescriptor> const& current);
 ThrowCompletionOr<Object*> get_prototype_from_constructor(VM&, FunctionObject const& constructor, Object* (Intrinsics::*intrinsic_default_prototype)());
diff --git a/Userland/Libraries/LibJS/Runtime/BoundFunction.h b/Userland/Libraries/LibJS/Runtime/BoundFunction.h
index b139dcae44f..bf2b251eb8e 100644
--- a/Userland/Libraries/LibJS/Runtime/BoundFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/BoundFunction.h
@@ -22,7 +22,7 @@ public:
     virtual ThrowCompletionOr<Value> internal_call(Value this_argument, MarkedVector<Value> arguments_list) override;
     virtual ThrowCompletionOr<NonnullGCPtr<Object>> internal_construct(MarkedVector<Value> arguments_list, FunctionObject& new_target) override;
 
-    virtual FlyString const& name() const override { return m_name; }
+    virtual DeprecatedFlyString const& name() const override { return m_name; }
     virtual bool is_strict_mode() const override { return m_bound_target_function->is_strict_mode(); }
     virtual bool has_constructor() const override { return m_bound_target_function->has_constructor(); }
 
@@ -39,7 +39,7 @@ private:
     Value m_bound_this;                                  // [[BoundThis]]
     Vector<Value> m_bound_arguments;                     // [[BoundArguments]]
 
-    FlyString m_name;
+    DeprecatedFlyString m_name;
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
index 8e9301cbeac..34f7dfed23f 100644
--- a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
+++ b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Runtime/PropertyKey.h>
 
diff --git a/Userland/Libraries/LibJS/Runtime/Completion.h b/Userland/Libraries/LibJS/Runtime/Completion.h
index 0203b642f6f..d1f226e6472 100644
--- a/Userland/Libraries/LibJS/Runtime/Completion.h
+++ b/Userland/Libraries/LibJS/Runtime/Completion.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Optional.h>
 #include <AK/Try.h>
 #include <AK/Variant.h>
@@ -40,7 +40,7 @@ public:
         Throw,
     };
 
-    ALWAYS_INLINE Completion(Type type, Optional<Value> value, Optional<FlyString> target)
+    ALWAYS_INLINE Completion(Type type, Optional<Value> value, Optional<DeprecatedFlyString> target)
         : m_type(type)
         , m_value(move(value))
         , m_target(move(target))
@@ -81,8 +81,8 @@ public:
     }
     [[nodiscard]] Optional<Value>& value() { return m_value; }
     [[nodiscard]] Optional<Value> const& value() const { return m_value; }
-    [[nodiscard]] Optional<FlyString>& target() { return m_target; }
-    [[nodiscard]] Optional<FlyString> const& target() const { return m_target; }
+    [[nodiscard]] Optional<DeprecatedFlyString>& target() { return m_target; }
+    [[nodiscard]] Optional<DeprecatedFlyString> const& target() const { return m_target; }
 
     // "abrupt completion refers to any completion with a [[Type]] value other than normal"
     [[nodiscard]] bool is_abrupt() const { return m_type != Type::Normal; }
@@ -127,9 +127,9 @@ private:
         return m_type == Type::Empty;
     }
 
-    Type m_type { Type::Normal }; // [[Type]]
-    Optional<Value> m_value;      // [[Value]]
-    Optional<FlyString> m_target; // [[Target]]
+    Type m_type { Type::Normal };           // [[Type]]
+    Optional<Value> m_value;                // [[Value]]
+    Optional<DeprecatedFlyString> m_target; // [[Target]]
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
index 0449887535c..d427780ed99 100644
--- a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.cpp
@@ -45,7 +45,7 @@ void DeclarativeEnvironment::visit_edges(Visitor& visitor)
 }
 
 // 9.1.1.1.1 HasBinding ( N ), https://tc39.es/ecma262/#sec-declarative-environment-records-hasbinding-n
-ThrowCompletionOr<bool> DeclarativeEnvironment::has_binding(FlyString const& name, Optional<size_t>* out_index) const
+ThrowCompletionOr<bool> DeclarativeEnvironment::has_binding(DeprecatedFlyString const& name, Optional<size_t>* out_index) const
 {
     auto binding_and_index = find_binding_and_index(name);
     if (!binding_and_index.has_value())
@@ -56,7 +56,7 @@ ThrowCompletionOr<bool> DeclarativeEnvironment::has_binding(FlyString const& nam
 }
 
 // 9.1.1.1.2 CreateMutableBinding ( N, D ), https://tc39.es/ecma262/#sec-declarative-environment-records-createmutablebinding-n-d
-ThrowCompletionOr<void> DeclarativeEnvironment::create_mutable_binding(VM&, FlyString const& name, bool can_be_deleted)
+ThrowCompletionOr<void> DeclarativeEnvironment::create_mutable_binding(VM&, DeprecatedFlyString const& name, bool can_be_deleted)
 {
     // 1. Assert: envRec does not already have a binding for N.
     // NOTE: We skip this to avoid O(n) traversal of m_bindings.
@@ -76,7 +76,7 @@ ThrowCompletionOr<void> DeclarativeEnvironment::create_mutable_binding(VM&, FlyS
 }
 
 // 9.1.1.1.3 CreateImmutableBinding ( N, S ), https://tc39.es/ecma262/#sec-declarative-environment-records-createimmutablebinding-n-s
-ThrowCompletionOr<void> DeclarativeEnvironment::create_immutable_binding(VM&, FlyString const& name, bool strict)
+ThrowCompletionOr<void> DeclarativeEnvironment::create_immutable_binding(VM&, DeprecatedFlyString const& name, bool strict)
 {
     // 1. Assert: envRec does not already have a binding for N.
     // NOTE: We skip this to avoid O(n) traversal of m_bindings.
@@ -96,7 +96,7 @@ ThrowCompletionOr<void> DeclarativeEnvironment::create_immutable_binding(VM&, Fl
 }
 
 // 9.1.1.1.4 InitializeBinding ( N, V ), https://tc39.es/ecma262/#sec-declarative-environment-records-initializebinding-n-v
-ThrowCompletionOr<void> DeclarativeEnvironment::initialize_binding(VM& vm, FlyString const& name, Value value)
+ThrowCompletionOr<void> DeclarativeEnvironment::initialize_binding(VM& vm, DeprecatedFlyString const& name, Value value)
 {
     auto binding_and_index = find_binding_and_index(name);
     VERIFY(binding_and_index.has_value());
@@ -120,7 +120,7 @@ ThrowCompletionOr<void> DeclarativeEnvironment::initialize_binding_direct(VM&, B
 }
 
 // 9.1.1.1.5 SetMutableBinding ( N, V, S ), https://tc39.es/ecma262/#sec-declarative-environment-records-setmutablebinding-n-v-s
-ThrowCompletionOr<void> DeclarativeEnvironment::set_mutable_binding(VM& vm, FlyString const& name, Value value, bool strict)
+ThrowCompletionOr<void> DeclarativeEnvironment::set_mutable_binding(VM& vm, DeprecatedFlyString const& name, Value value, bool strict)
 {
     // 1. If envRec does not have a binding for N, then
     auto binding_and_index = find_binding_and_index(name);
@@ -170,7 +170,7 @@ ThrowCompletionOr<void> DeclarativeEnvironment::set_mutable_binding_direct(VM& v
 }
 
 // 9.1.1.1.6 GetBindingValue ( N, S ), https://tc39.es/ecma262/#sec-declarative-environment-records-getbindingvalue-n-s
-ThrowCompletionOr<Value> DeclarativeEnvironment::get_binding_value(VM& vm, FlyString const& name, bool strict)
+ThrowCompletionOr<Value> DeclarativeEnvironment::get_binding_value(VM& vm, DeprecatedFlyString const& name, bool strict)
 {
     // 1. Assert: envRec has a binding for N.
     auto binding_and_index = find_binding_and_index(name);
@@ -196,7 +196,7 @@ ThrowCompletionOr<Value> DeclarativeEnvironment::get_binding_value_direct(VM&, B
 }
 
 // 9.1.1.1.7 DeleteBinding ( N ), https://tc39.es/ecma262/#sec-declarative-environment-records-deletebinding-n
-ThrowCompletionOr<bool> DeclarativeEnvironment::delete_binding(VM&, FlyString const& name)
+ThrowCompletionOr<bool> DeclarativeEnvironment::delete_binding(VM&, DeprecatedFlyString const& name)
 {
     // 1. Assert: envRec has a binding for the name that is the value of N.
     auto binding_and_index = find_binding_and_index(name);
@@ -214,7 +214,7 @@ ThrowCompletionOr<bool> DeclarativeEnvironment::delete_binding(VM&, FlyString co
     return true;
 }
 
-ThrowCompletionOr<void> DeclarativeEnvironment::initialize_or_set_mutable_binding(VM& vm, FlyString const& name, Value value)
+ThrowCompletionOr<void> DeclarativeEnvironment::initialize_or_set_mutable_binding(VM& vm, DeprecatedFlyString const& name, Value value)
 {
     auto binding_and_index = find_binding_and_index(name);
     VERIFY(binding_and_index.has_value());
@@ -226,7 +226,7 @@ ThrowCompletionOr<void> DeclarativeEnvironment::initialize_or_set_mutable_bindin
     return {};
 }
 
-void DeclarativeEnvironment::initialize_or_set_mutable_binding(Badge<ScopeNode>, VM& vm, FlyString const& name, Value value)
+void DeclarativeEnvironment::initialize_or_set_mutable_binding(Badge<ScopeNode>, VM& vm, DeprecatedFlyString const& name, Value value)
 {
     MUST(initialize_or_set_mutable_binding(vm, name, value));
 }
diff --git a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
index 18a905d5311..c4c844e0a8d 100644
--- a/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/DeclarativeEnvironment.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/HashMap.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Environment.h>
@@ -18,7 +18,7 @@ class DeclarativeEnvironment : public Environment {
     JS_ENVIRONMENT(DeclarativeEnvironment, Environment);
 
     struct Binding {
-        FlyString name;
+        DeprecatedFlyString name;
         Value value;
         bool strict { false };
         bool mutable_ { false };
@@ -31,21 +31,21 @@ public:
 
     virtual ~DeclarativeEnvironment() override = default;
 
-    virtual ThrowCompletionOr<bool> has_binding(FlyString const& name, Optional<size_t>* = nullptr) const override;
-    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, FlyString const& name, bool can_be_deleted) override;
-    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<void> initialize_binding(VM&, FlyString const& name, Value) override;
-    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, FlyString const& name, Value, bool strict) override;
-    virtual ThrowCompletionOr<Value> get_binding_value(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<bool> delete_binding(VM&, FlyString const& name) override;
+    virtual ThrowCompletionOr<bool> has_binding(DeprecatedFlyString const& name, Optional<size_t>* = nullptr) const override;
+    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, DeprecatedFlyString const& name, bool can_be_deleted) override;
+    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<void> initialize_binding(VM&, DeprecatedFlyString const& name, Value) override;
+    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, DeprecatedFlyString const& name, Value, bool strict) override;
+    virtual ThrowCompletionOr<Value> get_binding_value(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<bool> delete_binding(VM&, DeprecatedFlyString const& name) override;
 
-    void initialize_or_set_mutable_binding(Badge<ScopeNode>, VM&, FlyString const& name, Value value);
-    ThrowCompletionOr<void> initialize_or_set_mutable_binding(VM&, FlyString const& name, Value value);
+    void initialize_or_set_mutable_binding(Badge<ScopeNode>, VM&, DeprecatedFlyString const& name, Value value);
+    ThrowCompletionOr<void> initialize_or_set_mutable_binding(VM&, DeprecatedFlyString const& name, Value value);
 
     // This is not a method defined in the spec! Do not use this in any LibJS (or other spec related) code.
-    [[nodiscard]] Vector<FlyString> bindings() const
+    [[nodiscard]] Vector<DeprecatedFlyString> bindings() const
     {
-        Vector<FlyString> names;
+        Vector<DeprecatedFlyString> names;
         names.ensure_capacity(m_bindings.size());
 
         for (auto const& binding : m_bindings)
@@ -101,7 +101,7 @@ protected:
 
     friend class ModuleEnvironment;
 
-    virtual Optional<BindingAndIndex> find_binding_and_index(FlyString const& name) const
+    virtual Optional<BindingAndIndex> find_binding_and_index(DeprecatedFlyString const& name) const
     {
         auto it = m_bindings.find_if([&](auto const& binding) {
             return binding.name == name;
diff --git a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
index a5a9cdfbbdf..2c7c2708865 100644
--- a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
@@ -28,7 +28,7 @@
 
 namespace JS {
 
-NonnullGCPtr<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, FlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
+NonnullGCPtr<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, DeprecatedFlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
 {
     Object* prototype = nullptr;
     switch (kind) {
@@ -48,12 +48,12 @@ NonnullGCPtr<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& r
     return realm.heap().allocate<ECMAScriptFunctionObject>(realm, move(name), move(source_text), ecmascript_code, move(parameters), m_function_length, parent_environment, private_environment, *prototype, kind, is_strict, might_need_arguments_object, contains_direct_call_to_eval, is_arrow_function, move(class_field_initializer_name));
 }
 
-NonnullGCPtr<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, FlyString name, Object& prototype, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
+NonnullGCPtr<ECMAScriptFunctionObject> ECMAScriptFunctionObject::create(Realm& realm, DeprecatedFlyString name, Object& prototype, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind kind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
 {
     return realm.heap().allocate<ECMAScriptFunctionObject>(realm, move(name), move(source_text), ecmascript_code, move(parameters), m_function_length, parent_environment, private_environment, prototype, kind, is_strict, might_need_arguments_object, contains_direct_call_to_eval, is_arrow_function, move(class_field_initializer_name));
 }
 
-ECMAScriptFunctionObject::ECMAScriptFunctionObject(FlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> formal_parameters, i32 function_length, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind kind, bool strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
+ECMAScriptFunctionObject::ECMAScriptFunctionObject(DeprecatedFlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> formal_parameters, i32 function_length, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind kind, bool strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name)
     : FunctionObject(prototype)
     , m_name(move(name))
     , m_function_length(function_length)
@@ -91,7 +91,7 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(FlyString name, DeprecatedStr
             return false;
         if (parameter.default_value)
             return false;
-        if (!parameter.binding.template has<FlyString>())
+        if (!parameter.binding.template has<DeprecatedFlyString>())
             return false;
         return true;
     });
@@ -338,13 +338,13 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
     // FIXME: Maybe compute has duplicates at parse time? (We need to anyway since it's an error in some cases)
 
     bool has_duplicates = false;
-    HashTable<FlyString> parameter_names;
+    HashTable<DeprecatedFlyString> parameter_names;
     for (auto& parameter : m_formal_parameters) {
         if (parameter.default_value)
             has_parameter_expressions = true;
 
         parameter.binding.visit(
-            [&](FlyString const& name) {
+            [&](DeprecatedFlyString const& name) {
                 if (parameter_names.set(name) != AK::HashSetResult::InsertedNewEntry)
                     has_duplicates = true;
             },
@@ -367,7 +367,7 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
     if (parameter_names.contains(vm.names.arguments.as_string()))
         arguments_object_needed = false;
 
-    HashTable<FlyString> function_names;
+    HashTable<DeprecatedFlyString> function_names;
     Vector<FunctionDeclaration const&> functions_to_initialize;
 
     if (scope_body) {
@@ -463,7 +463,7 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
 
                 Environment* used_environment = has_duplicates ? nullptr : environment;
 
-                if constexpr (IsSame<FlyString const&, decltype(param)>) {
+                if constexpr (IsSame<DeprecatedFlyString const&, decltype(param)>) {
                     Reference reference = TRY(vm.resolve_binding(param, used_environment));
                     // Here the difference from hasDuplicates is important
                     if (has_duplicates)
@@ -479,7 +479,7 @@ ThrowCompletionOr<void> ECMAScriptFunctionObject::function_declaration_instantia
 
     GCPtr<Environment> var_environment;
 
-    HashTable<FlyString> instantiated_var_names;
+    HashTable<DeprecatedFlyString> instantiated_var_names;
     if (scope_body)
         instantiated_var_names.ensure_capacity(scope_body->var_declaration_count());
 
@@ -911,7 +911,7 @@ Completion ECMAScriptFunctionObject::ordinary_call_evaluate_body()
     VERIFY_NOT_REACHED();
 }
 
-void ECMAScriptFunctionObject::set_name(FlyString const& name)
+void ECMAScriptFunctionObject::set_name(DeprecatedFlyString const& name)
 {
     VERIFY(!name.is_null());
     auto& vm = this->vm();
diff --git a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
index ca7c82ccd6e..ef196ebf557 100644
--- a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
+++ b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
@@ -32,8 +32,8 @@ public:
         Global,
     };
 
-    static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, FlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
-    static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, FlyString name, Object& prototype, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
+    static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
+    static NonnullGCPtr<ECMAScriptFunctionObject> create(Realm&, DeprecatedFlyString name, Object& prototype, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, FunctionKind, bool is_strict, bool might_need_arguments_object = true, bool contains_direct_call_to_eval = true, bool is_arrow_function = false, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name = {});
 
     virtual void initialize(Realm&) override;
     virtual ~ECMAScriptFunctionObject() override = default;
@@ -46,8 +46,8 @@ public:
     Statement const& ecmascript_code() const { return m_ecmascript_code; }
     Vector<FunctionParameter> const& formal_parameters() const { return m_formal_parameters; };
 
-    virtual FlyString const& name() const override { return m_name; };
-    void set_name(FlyString const& name);
+    virtual DeprecatedFlyString const& name() const override { return m_name; };
+    void set_name(DeprecatedFlyString const& name);
 
     void set_is_class_constructor() { m_is_class_constructor = true; };
 
@@ -93,7 +93,7 @@ protected:
     virtual Completion ordinary_call_evaluate_body();
 
 private:
-    ECMAScriptFunctionObject(FlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name);
+    ECMAScriptFunctionObject(DeprecatedFlyString name, DeprecatedString source_text, Statement const& ecmascript_code, Vector<FunctionParameter> parameters, i32 m_function_length, Environment* parent_environment, PrivateEnvironment* private_environment, Object& prototype, FunctionKind, bool is_strict, bool might_need_arguments_object, bool contains_direct_call_to_eval, bool is_arrow_function, Variant<PropertyKey, PrivateName, Empty> class_field_initializer_name);
 
     virtual bool is_ecmascript_function_object() const override { return true; }
     virtual void visit_edges(Visitor&) override;
@@ -105,7 +105,7 @@ private:
 
     ThrowCompletionOr<void> function_declaration_instantiation(Interpreter*);
 
-    FlyString m_name;
+    DeprecatedFlyString m_name;
     OwnPtr<Bytecode::Executable> m_bytecode_executable;
     Vector<OwnPtr<Bytecode::Executable>> m_default_parameter_bytecode_executables;
     i32 m_function_length { 0 };
diff --git a/Userland/Libraries/LibJS/Runtime/Environment.h b/Userland/Libraries/LibJS/Runtime/Environment.h
index 9073eeab053..74388d74291 100644
--- a/Userland/Libraries/LibJS/Runtime/Environment.h
+++ b/Userland/Libraries/LibJS/Runtime/Environment.h
@@ -28,13 +28,13 @@ public:
 
     virtual Object* with_base_object() const { return nullptr; }
 
-    virtual ThrowCompletionOr<bool> has_binding([[maybe_unused]] FlyString const& name, [[maybe_unused]] Optional<size_t>* out_index = nullptr) const { return false; }
-    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, [[maybe_unused]] FlyString const& name, [[maybe_unused]] bool can_be_deleted) { return {}; }
-    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, [[maybe_unused]] FlyString const& name, [[maybe_unused]] bool strict) { return {}; }
-    virtual ThrowCompletionOr<void> initialize_binding(VM&, [[maybe_unused]] FlyString const& name, Value) { return {}; }
-    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, [[maybe_unused]] FlyString const& name, Value, [[maybe_unused]] bool strict) { return {}; }
-    virtual ThrowCompletionOr<Value> get_binding_value(VM&, [[maybe_unused]] FlyString const& name, [[maybe_unused]] bool strict) { return Value {}; }
-    virtual ThrowCompletionOr<bool> delete_binding(VM&, [[maybe_unused]] FlyString const& name) { return false; }
+    virtual ThrowCompletionOr<bool> has_binding([[maybe_unused]] DeprecatedFlyString const& name, [[maybe_unused]] Optional<size_t>* out_index = nullptr) const { return false; }
+    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, [[maybe_unused]] DeprecatedFlyString const& name, [[maybe_unused]] bool can_be_deleted) { return {}; }
+    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, [[maybe_unused]] DeprecatedFlyString const& name, [[maybe_unused]] bool strict) { return {}; }
+    virtual ThrowCompletionOr<void> initialize_binding(VM&, [[maybe_unused]] DeprecatedFlyString const& name, Value) { return {}; }
+    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, [[maybe_unused]] DeprecatedFlyString const& name, Value, [[maybe_unused]] bool strict) { return {}; }
+    virtual ThrowCompletionOr<Value> get_binding_value(VM&, [[maybe_unused]] DeprecatedFlyString const& name, [[maybe_unused]] bool strict) { return Value {}; }
+    virtual ThrowCompletionOr<bool> delete_binding(VM&, [[maybe_unused]] DeprecatedFlyString const& name) { return false; }
 
     // [[OuterEnv]]
     Environment* outer_environment() { return m_outer_environment; }
diff --git a/Userland/Libraries/LibJS/Runtime/Error.h b/Userland/Libraries/LibJS/Runtime/Error.h
index 994aa767599..0422003e167 100644
--- a/Userland/Libraries/LibJS/Runtime/Error.h
+++ b/Userland/Libraries/LibJS/Runtime/Error.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/SourceRange.h>
@@ -15,7 +15,7 @@
 namespace JS {
 
 struct TracebackFrame {
-    FlyString function_name;
+    DeprecatedFlyString function_name;
     SourceRange source_range;
 };
 
diff --git a/Userland/Libraries/LibJS/Runtime/ExecutionContext.h b/Userland/Libraries/LibJS/Runtime/ExecutionContext.h
index 4397604b0bc..aea49861609 100644
--- a/Userland/Libraries/LibJS/Runtime/ExecutionContext.h
+++ b/Userland/Libraries/LibJS/Runtime/ExecutionContext.h
@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/WeakPtr.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Heap/MarkedVector.h>
@@ -43,7 +43,7 @@ public:
     Cell* context_owner { nullptr };
 
     ASTNode const* current_node { nullptr };
-    FlyString function_name;
+    DeprecatedFlyString function_name;
     Value this_value;
     MarkedVector<Value> arguments;
     bool is_strict_mode { false };
diff --git a/Userland/Libraries/LibJS/Runtime/FunctionObject.h b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
index b039b89ea42..6fc6991a793 100644
--- a/Userland/Libraries/LibJS/Runtime/FunctionObject.h
+++ b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
@@ -27,7 +27,7 @@ public:
     virtual ThrowCompletionOr<Value> internal_call(Value this_argument, MarkedVector<Value> arguments_list) = 0;
     virtual ThrowCompletionOr<NonnullGCPtr<Object>> internal_construct([[maybe_unused]] MarkedVector<Value> arguments_list, [[maybe_unused]] FunctionObject& new_target) { VERIFY_NOT_REACHED(); }
 
-    virtual FlyString const& name() const = 0;
+    virtual DeprecatedFlyString const& name() const = 0;
 
     void set_function_name(Variant<PropertyKey, PrivateName> const& name_arg, Optional<StringView> const& prefix = {});
     void set_function_length(double length);
diff --git a/Userland/Libraries/LibJS/Runtime/FunctionPrototype.h b/Userland/Libraries/LibJS/Runtime/FunctionPrototype.h
index 0fd04665ed8..77919d5abc1 100644
--- a/Userland/Libraries/LibJS/Runtime/FunctionPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/FunctionPrototype.h
@@ -18,7 +18,7 @@ public:
     virtual ~FunctionPrototype() override = default;
 
     virtual ThrowCompletionOr<Value> internal_call(Value this_argument, MarkedVector<Value> arguments_list) override;
-    virtual FlyString const& name() const override { return m_name; }
+    virtual DeprecatedFlyString const& name() const override { return m_name; }
 
 private:
     explicit FunctionPrototype(Realm&);
@@ -31,7 +31,7 @@ private:
 
     // Totally unnecessary, but sadly still necessary.
     // TODO: Get rid of the pointless name() method.
-    FlyString m_name { "FunctionPrototype" };
+    DeprecatedFlyString m_name { "FunctionPrototype" };
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
index 64d766525db..2fada09a3d0 100644
--- a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.cpp
@@ -39,7 +39,7 @@ ThrowCompletionOr<Value> GlobalEnvironment::get_this_binding(VM&) const
 }
 
 // 9.1.1.4.1 HasBinding ( N ), https://tc39.es/ecma262/#sec-global-environment-records-hasbinding-n
-ThrowCompletionOr<bool> GlobalEnvironment::has_binding(FlyString const& name, Optional<size_t>* out_index) const
+ThrowCompletionOr<bool> GlobalEnvironment::has_binding(DeprecatedFlyString const& name, Optional<size_t>* out_index) const
 {
     if (out_index)
         *out_index = EnvironmentCoordinate::global_marker;
@@ -55,7 +55,7 @@ ThrowCompletionOr<bool> GlobalEnvironment::has_binding(FlyString const& name, Op
 }
 
 // 9.1.1.4.2 CreateMutableBinding ( N, D ), https://tc39.es/ecma262/#sec-global-environment-records-createmutablebinding-n-d
-ThrowCompletionOr<void> GlobalEnvironment::create_mutable_binding(VM& vm, FlyString const& name, bool can_be_deleted)
+ThrowCompletionOr<void> GlobalEnvironment::create_mutable_binding(VM& vm, DeprecatedFlyString const& name, bool can_be_deleted)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, throw a TypeError exception.
@@ -67,7 +67,7 @@ ThrowCompletionOr<void> GlobalEnvironment::create_mutable_binding(VM& vm, FlyStr
 }
 
 // 9.1.1.4.3 CreateImmutableBinding ( N, S ), https://tc39.es/ecma262/#sec-global-environment-records-createimmutablebinding-n-s
-ThrowCompletionOr<void> GlobalEnvironment::create_immutable_binding(VM& vm, FlyString const& name, bool strict)
+ThrowCompletionOr<void> GlobalEnvironment::create_immutable_binding(VM& vm, DeprecatedFlyString const& name, bool strict)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, throw a TypeError exception.
@@ -79,7 +79,7 @@ ThrowCompletionOr<void> GlobalEnvironment::create_immutable_binding(VM& vm, FlyS
 }
 
 // 9.1.1.4.4 InitializeBinding ( N, V ), https://tc39.es/ecma262/#sec-global-environment-records-initializebinding-n-v
-ThrowCompletionOr<void> GlobalEnvironment::initialize_binding(VM& vm, FlyString const& name, Value value)
+ThrowCompletionOr<void> GlobalEnvironment::initialize_binding(VM& vm, DeprecatedFlyString const& name, Value value)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, then
@@ -95,7 +95,7 @@ ThrowCompletionOr<void> GlobalEnvironment::initialize_binding(VM& vm, FlyString
 }
 
 // 9.1.1.4.5 SetMutableBinding ( N, V, S ), https://tc39.es/ecma262/#sec-global-environment-records-setmutablebinding-n-v-s
-ThrowCompletionOr<void> GlobalEnvironment::set_mutable_binding(VM& vm, FlyString const& name, Value value, bool strict)
+ThrowCompletionOr<void> GlobalEnvironment::set_mutable_binding(VM& vm, DeprecatedFlyString const& name, Value value, bool strict)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, then
@@ -110,7 +110,7 @@ ThrowCompletionOr<void> GlobalEnvironment::set_mutable_binding(VM& vm, FlyString
 }
 
 // 9.1.1.4.6 GetBindingValue ( N, S ), https://tc39.es/ecma262/#sec-global-environment-records-getbindingvalue-n-s
-ThrowCompletionOr<Value> GlobalEnvironment::get_binding_value(VM& vm, FlyString const& name, bool strict)
+ThrowCompletionOr<Value> GlobalEnvironment::get_binding_value(VM& vm, DeprecatedFlyString const& name, bool strict)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, then
@@ -125,7 +125,7 @@ ThrowCompletionOr<Value> GlobalEnvironment::get_binding_value(VM& vm, FlyString
 }
 
 // 9.1.1.4.7 DeleteBinding ( N ), https://tc39.es/ecma262/#sec-global-environment-records-deletebinding-n
-ThrowCompletionOr<bool> GlobalEnvironment::delete_binding(VM& vm, FlyString const& name)
+ThrowCompletionOr<bool> GlobalEnvironment::delete_binding(VM& vm, DeprecatedFlyString const& name)
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. If ! DclRec.HasBinding(N) is true, then
@@ -161,7 +161,7 @@ ThrowCompletionOr<bool> GlobalEnvironment::delete_binding(VM& vm, FlyString cons
 }
 
 // 9.1.1.4.12 HasVarDeclaration ( N ), https://tc39.es/ecma262/#sec-hasvardeclaration
-bool GlobalEnvironment::has_var_declaration(FlyString const& name) const
+bool GlobalEnvironment::has_var_declaration(DeprecatedFlyString const& name) const
 {
     // 1. Let varDeclaredNames be envRec.[[VarNames]].
     // 2. If varDeclaredNames contains N, return true.
@@ -170,7 +170,7 @@ bool GlobalEnvironment::has_var_declaration(FlyString const& name) const
 }
 
 // 9.1.1.4.13 HasLexicalDeclaration ( N ), https://tc39.es/ecma262/#sec-haslexicaldeclaration
-bool GlobalEnvironment::has_lexical_declaration(FlyString const& name) const
+bool GlobalEnvironment::has_lexical_declaration(DeprecatedFlyString const& name) const
 {
     // 1. Let DclRec be envRec.[[DeclarativeRecord]].
     // 2. Return ! DclRec.HasBinding(N).
@@ -178,7 +178,7 @@ bool GlobalEnvironment::has_lexical_declaration(FlyString const& name) const
 }
 
 // 9.1.1.4.14 HasRestrictedGlobalProperty ( N ), https://tc39.es/ecma262/#sec-hasrestrictedglobalproperty
-ThrowCompletionOr<bool> GlobalEnvironment::has_restricted_global_property(FlyString const& name) const
+ThrowCompletionOr<bool> GlobalEnvironment::has_restricted_global_property(DeprecatedFlyString const& name) const
 {
     // 1. Let ObjRec be envRec.[[ObjectRecord]].
     // 2. Let globalObject be ObjRec.[[BindingObject]].
@@ -200,7 +200,7 @@ ThrowCompletionOr<bool> GlobalEnvironment::has_restricted_global_property(FlyStr
 }
 
 // 9.1.1.4.15 CanDeclareGlobalVar ( N ), https://tc39.es/ecma262/#sec-candeclareglobalvar
-ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_var(FlyString const& name) const
+ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_var(DeprecatedFlyString const& name) const
 {
     // 1. Let ObjRec be envRec.[[ObjectRecord]].
     // 2. Let globalObject be ObjRec.[[BindingObject]].
@@ -218,7 +218,7 @@ ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_var(FlyString cons
 }
 
 // 9.1.1.4.16 CanDeclareGlobalFunction ( N ), https://tc39.es/ecma262/#sec-candeclareglobalfunction
-ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_function(FlyString const& name) const
+ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_function(DeprecatedFlyString const& name) const
 {
     // 1. Let ObjRec be envRec.[[ObjectRecord]].
     // 2. Let globalObject be ObjRec.[[BindingObject]].
@@ -244,7 +244,7 @@ ThrowCompletionOr<bool> GlobalEnvironment::can_declare_global_function(FlyString
 }
 
 // 9.1.1.4.17 CreateGlobalVarBinding ( N, D ), https://tc39.es/ecma262/#sec-createglobalvarbinding
-ThrowCompletionOr<void> GlobalEnvironment::create_global_var_binding(FlyString const& name, bool can_be_deleted)
+ThrowCompletionOr<void> GlobalEnvironment::create_global_var_binding(DeprecatedFlyString const& name, bool can_be_deleted)
 {
     auto& vm = this->vm();
 
@@ -279,7 +279,7 @@ ThrowCompletionOr<void> GlobalEnvironment::create_global_var_binding(FlyString c
 }
 
 // 9.1.1.4.18 CreateGlobalFunctionBinding ( N, V, D ), https://tc39.es/ecma262/#sec-createglobalfunctionbinding
-ThrowCompletionOr<void> GlobalEnvironment::create_global_function_binding(FlyString const& name, Value value, bool can_be_deleted)
+ThrowCompletionOr<void> GlobalEnvironment::create_global_function_binding(DeprecatedFlyString const& name, Value value, bool can_be_deleted)
 {
     // 1. Let ObjRec be envRec.[[ObjectRecord]].
     // 2. Let globalObject be ObjRec.[[BindingObject]].
diff --git a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.h b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.h
index 8f7cf688f78..65ed8437250 100644
--- a/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/GlobalEnvironment.h
@@ -17,25 +17,25 @@ public:
     virtual bool has_this_binding() const final { return true; }
     virtual ThrowCompletionOr<Value> get_this_binding(VM&) const final;
 
-    virtual ThrowCompletionOr<bool> has_binding(FlyString const& name, Optional<size_t>* = nullptr) const override;
-    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, FlyString const& name, bool can_be_deleted) override;
-    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<void> initialize_binding(VM&, FlyString const& name, Value) override;
-    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, FlyString const& name, Value, bool strict) override;
-    virtual ThrowCompletionOr<Value> get_binding_value(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<bool> delete_binding(VM&, FlyString const& name) override;
+    virtual ThrowCompletionOr<bool> has_binding(DeprecatedFlyString const& name, Optional<size_t>* = nullptr) const override;
+    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, DeprecatedFlyString const& name, bool can_be_deleted) override;
+    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<void> initialize_binding(VM&, DeprecatedFlyString const& name, Value) override;
+    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, DeprecatedFlyString const& name, Value, bool strict) override;
+    virtual ThrowCompletionOr<Value> get_binding_value(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<bool> delete_binding(VM&, DeprecatedFlyString const& name) override;
 
     ObjectEnvironment& object_record() { return *m_object_record; }
     Object& global_this_value() { return *m_global_this_value; }
     DeclarativeEnvironment& declarative_record() { return *m_declarative_record; }
 
-    bool has_var_declaration(FlyString const& name) const;
-    bool has_lexical_declaration(FlyString const& name) const;
-    ThrowCompletionOr<bool> has_restricted_global_property(FlyString const& name) const;
-    ThrowCompletionOr<bool> can_declare_global_var(FlyString const& name) const;
-    ThrowCompletionOr<bool> can_declare_global_function(FlyString const& name) const;
-    ThrowCompletionOr<void> create_global_var_binding(FlyString const& name, bool can_be_deleted);
-    ThrowCompletionOr<void> create_global_function_binding(FlyString const& name, Value, bool can_be_deleted);
+    bool has_var_declaration(DeprecatedFlyString const& name) const;
+    bool has_lexical_declaration(DeprecatedFlyString const& name) const;
+    ThrowCompletionOr<bool> has_restricted_global_property(DeprecatedFlyString const& name) const;
+    ThrowCompletionOr<bool> can_declare_global_var(DeprecatedFlyString const& name) const;
+    ThrowCompletionOr<bool> can_declare_global_function(DeprecatedFlyString const& name) const;
+    ThrowCompletionOr<void> create_global_var_binding(DeprecatedFlyString const& name, bool can_be_deleted);
+    ThrowCompletionOr<void> create_global_function_binding(DeprecatedFlyString const& name, Value, bool can_be_deleted);
 
 private:
     GlobalEnvironment(Object&, Object& this_value);
@@ -46,7 +46,7 @@ private:
     ObjectEnvironment* m_object_record { nullptr };           // [[ObjectRecord]]
     Object* m_global_this_value { nullptr };                  // [[GlobalThisValue]]
     DeclarativeEnvironment* m_declarative_record { nullptr }; // [[DeclarativeRecord]]
-    Vector<FlyString> m_var_names;                            // [[VarNames]]
+    Vector<DeprecatedFlyString> m_var_names;                  // [[VarNames]]
 };
 
 template<>
diff --git a/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
index 8c2c7f5270b..ba2a2fa38b4 100644
--- a/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.cpp
@@ -18,7 +18,7 @@ ModuleEnvironment::ModuleEnvironment(Environment* outer_environment)
 }
 
 // 9.1.1.5.1 GetBindingValue ( N, S ), https://tc39.es/ecma262/#sec-module-environment-records-getbindingvalue-n-s
-ThrowCompletionOr<Value> ModuleEnvironment::get_binding_value(VM& vm, FlyString const& name, bool strict)
+ThrowCompletionOr<Value> ModuleEnvironment::get_binding_value(VM& vm, DeprecatedFlyString const& name, bool strict)
 {
     // 1. Assert: S is true.
     VERIFY(strict);
@@ -49,7 +49,7 @@ ThrowCompletionOr<Value> ModuleEnvironment::get_binding_value(VM& vm, FlyString
 }
 
 // 9.1.1.5.2 DeleteBinding ( N ), https://tc39.es/ecma262/#sec-module-environment-records-deletebinding-n
-ThrowCompletionOr<bool> ModuleEnvironment::delete_binding(VM&, FlyString const&)
+ThrowCompletionOr<bool> ModuleEnvironment::delete_binding(VM&, DeprecatedFlyString const&)
 {
     // The DeleteBinding concrete method of a module Environment Record is never used within this specification.
     VERIFY_NOT_REACHED();
@@ -63,7 +63,7 @@ ThrowCompletionOr<Value> ModuleEnvironment::get_this_binding(VM&) const
 }
 
 // 9.1.1.5.5 CreateImportBinding ( N, M, N2 ), https://tc39.es/ecma262/#sec-createimportbinding
-ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(FlyString name, Module* module, FlyString binding_name)
+ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(DeprecatedFlyString name, Module* module, DeprecatedFlyString binding_name)
 {
     // 1. Assert: envRec does not already have a binding for N.
     VERIFY(!get_indirect_binding(name));
@@ -80,7 +80,7 @@ ThrowCompletionOr<void> ModuleEnvironment::create_import_binding(FlyString name,
     return {};
 }
 
-ModuleEnvironment::IndirectBinding const* ModuleEnvironment::get_indirect_binding(FlyString const& name) const
+ModuleEnvironment::IndirectBinding const* ModuleEnvironment::get_indirect_binding(DeprecatedFlyString const& name) const
 {
     auto binding_or_end = m_indirect_bindings.find_if([&](IndirectBinding const& binding) {
         return binding.name == name;
@@ -91,7 +91,7 @@ ModuleEnvironment::IndirectBinding const* ModuleEnvironment::get_indirect_bindin
     return &(*binding_or_end);
 }
 
-Optional<ModuleEnvironment::BindingAndIndex> ModuleEnvironment::find_binding_and_index(FlyString const& name) const
+Optional<ModuleEnvironment::BindingAndIndex> ModuleEnvironment::find_binding_and_index(DeprecatedFlyString const& name) const
 {
     auto* indirect_binding = get_indirect_binding(name);
     if (indirect_binding != nullptr) {
diff --git a/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.h b/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.h
index 181da9134e5..03eee4b39fe 100644
--- a/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/ModuleEnvironment.h
@@ -21,11 +21,11 @@ public:
     //       in Table 18 and share the same specifications for all of those methods except for
     //       GetBindingValue, DeleteBinding, HasThisBinding and GetThisBinding.
     //       In addition, module Environment Records support the methods listed in Table 24.
-    virtual ThrowCompletionOr<Value> get_binding_value(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<bool> delete_binding(VM&, FlyString const& name) override;
+    virtual ThrowCompletionOr<Value> get_binding_value(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<bool> delete_binding(VM&, DeprecatedFlyString const& name) override;
     virtual bool has_this_binding() const final { return true; }
     virtual ThrowCompletionOr<Value> get_this_binding(VM&) const final;
-    ThrowCompletionOr<void> create_import_binding(FlyString name, Module* module, FlyString binding_name);
+    ThrowCompletionOr<void> create_import_binding(DeprecatedFlyString name, Module* module, DeprecatedFlyString binding_name);
 
 private:
     explicit ModuleEnvironment(Environment* outer_environment);
@@ -33,13 +33,13 @@ private:
     virtual void visit_edges(Visitor&) override;
 
     struct IndirectBinding {
-        FlyString name;
+        DeprecatedFlyString name;
         Module* module;
-        FlyString binding_name;
+        DeprecatedFlyString binding_name;
     };
-    IndirectBinding const* get_indirect_binding(FlyString const& name) const;
+    IndirectBinding const* get_indirect_binding(DeprecatedFlyString const& name) const;
 
-    virtual Optional<BindingAndIndex> find_binding_and_index(FlyString const& name) const override;
+    virtual Optional<BindingAndIndex> find_binding_and_index(DeprecatedFlyString const& name) const override;
 
     // FIXME: Since we always access this via the name this could be a map.
     Vector<IndirectBinding> m_indirect_bindings;
diff --git a/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp b/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
index 99244730496..7b5a18aed31 100644
--- a/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.cpp
@@ -10,14 +10,14 @@
 
 namespace JS {
 
-ModuleNamespaceObject::ModuleNamespaceObject(Realm& realm, Module* module, Vector<FlyString> exports)
+ModuleNamespaceObject::ModuleNamespaceObject(Realm& realm, Module* module, Vector<DeprecatedFlyString> exports)
     : Object(ConstructWithPrototypeTag::Tag, *realm.intrinsics().object_prototype())
     , m_module(module)
     , m_exports(move(exports))
 {
     // Note: We just perform step 6 of 10.4.6.12 ModuleNamespaceCreate ( module, exports ), https://tc39.es/ecma262/#sec-modulenamespacecreate
     // 6. Let sortedExports be a List whose elements are the elements of exports ordered as if an Array of the same values had been sorted using %Array.prototype.sort% using undefined as comparefn.
-    quick_sort(m_exports, [&](FlyString const& lhs, FlyString const& rhs) {
+    quick_sort(m_exports, [&](DeprecatedFlyString const& lhs, DeprecatedFlyString const& rhs) {
         return lhs.view() < rhs.view();
     });
 }
diff --git a/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.h b/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.h
index 8c72cfd4365..97f9e7440b4 100644
--- a/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.h
+++ b/Userland/Libraries/LibJS/Runtime/ModuleNamespaceObject.h
@@ -32,11 +32,11 @@ public:
     virtual void initialize(Realm&) override;
 
 private:
-    ModuleNamespaceObject(Realm&, Module* module, Vector<FlyString> exports);
+    ModuleNamespaceObject(Realm&, Module* module, Vector<DeprecatedFlyString> exports);
 
     // FIXME: UHHH how do we want to store this to avoid cycles but be safe??
-    Module* m_module;            // [[Module]]
-    Vector<FlyString> m_exports; // [[Exports]]
+    Module* m_module;                      // [[Module]]
+    Vector<DeprecatedFlyString> m_exports; // [[Exports]]
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/ModuleRequest.h b/Userland/Libraries/LibJS/Runtime/ModuleRequest.h
index 90fb7ab5f57..98dae53d0fe 100644
--- a/Userland/Libraries/LibJS/Runtime/ModuleRequest.h
+++ b/Userland/Libraries/LibJS/Runtime/ModuleRequest.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Vector.h>
 
 namespace JS {
@@ -20,20 +20,20 @@ struct ModuleRequest {
 
     ModuleRequest() = default;
 
-    explicit ModuleRequest(FlyString specifier)
+    explicit ModuleRequest(DeprecatedFlyString specifier)
         : module_specifier(move(specifier))
     {
     }
 
-    ModuleRequest(FlyString module_specifier, Vector<Assertion> assertions);
+    ModuleRequest(DeprecatedFlyString module_specifier, Vector<Assertion> assertions);
 
     void add_assertion(DeprecatedString key, DeprecatedString value)
     {
         assertions.empend(move(key), move(value));
     }
 
-    FlyString module_specifier;   // [[Specifier]]
-    Vector<Assertion> assertions; // [[Assertions]]
+    DeprecatedFlyString module_specifier; // [[Specifier]]
+    Vector<Assertion> assertions;         // [[Assertions]]
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp b/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
index 21c31d92a45..bb8427e2fcc 100644
--- a/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
+++ b/Userland/Libraries/LibJS/Runtime/NativeFunction.cpp
@@ -51,7 +51,7 @@ NonnullGCPtr<NativeFunction> NativeFunction::create(Realm& allocating_realm, Saf
     return function;
 }
 
-NonnullGCPtr<NativeFunction> NativeFunction::create(Realm& realm, FlyString const& name, SafeFunction<ThrowCompletionOr<Value>(VM&)> function)
+NonnullGCPtr<NativeFunction> NativeFunction::create(Realm& realm, DeprecatedFlyString const& name, SafeFunction<ThrowCompletionOr<Value>(VM&)> function)
 {
     return realm.heap().allocate<NativeFunction>(realm, name, move(function), *realm.intrinsics().function_prototype());
 }
@@ -73,7 +73,7 @@ NativeFunction::NativeFunction(Object& prototype)
 {
 }
 
-NativeFunction::NativeFunction(FlyString name, SafeFunction<ThrowCompletionOr<Value>(VM&)> native_function, Object& prototype)
+NativeFunction::NativeFunction(DeprecatedFlyString name, SafeFunction<ThrowCompletionOr<Value>(VM&)> native_function, Object& prototype)
     : FunctionObject(prototype)
     , m_name(move(name))
     , m_native_function(move(native_function))
@@ -81,7 +81,7 @@ NativeFunction::NativeFunction(FlyString name, SafeFunction<ThrowCompletionOr<Va
 {
 }
 
-NativeFunction::NativeFunction(FlyString name, Object& prototype)
+NativeFunction::NativeFunction(DeprecatedFlyString name, Object& prototype)
     : FunctionObject(prototype)
     , m_name(move(name))
     , m_realm(&prototype.shape().realm())
diff --git a/Userland/Libraries/LibJS/Runtime/NativeFunction.h b/Userland/Libraries/LibJS/Runtime/NativeFunction.h
index 62d9c41d75f..8c45ba38ec3 100644
--- a/Userland/Libraries/LibJS/Runtime/NativeFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/NativeFunction.h
@@ -21,7 +21,7 @@ class NativeFunction : public FunctionObject {
 
 public:
     static NonnullGCPtr<NativeFunction> create(Realm&, SafeFunction<ThrowCompletionOr<Value>(VM&)> behaviour, i32 length, PropertyKey const& name, Optional<Realm*> = {}, Optional<Object*> prototype = {}, Optional<StringView> const& prefix = {});
-    static NonnullGCPtr<NativeFunction> create(Realm&, FlyString const& name, SafeFunction<ThrowCompletionOr<Value>(VM&)>);
+    static NonnullGCPtr<NativeFunction> create(Realm&, DeprecatedFlyString const& name, SafeFunction<ThrowCompletionOr<Value>(VM&)>);
 
     virtual void initialize(Realm&) override { }
     virtual ~NativeFunction() override = default;
@@ -34,25 +34,25 @@ public:
     virtual ThrowCompletionOr<Value> call();
     virtual ThrowCompletionOr<NonnullGCPtr<Object>> construct(FunctionObject& new_target);
 
-    virtual FlyString const& name() const override { return m_name; };
+    virtual DeprecatedFlyString const& name() const override { return m_name; };
     virtual bool is_strict_mode() const override;
     virtual bool has_constructor() const override { return false; }
     virtual Realm* realm() const override { return m_realm; }
 
-    Optional<FlyString> const& initial_name() const { return m_initial_name; }
-    void set_initial_name(Badge<FunctionObject>, FlyString initial_name) { m_initial_name = move(initial_name); }
+    Optional<DeprecatedFlyString> const& initial_name() const { return m_initial_name; }
+    void set_initial_name(Badge<FunctionObject>, DeprecatedFlyString initial_name) { m_initial_name = move(initial_name); }
 
 protected:
-    NativeFunction(FlyString name, Object& prototype);
+    NativeFunction(DeprecatedFlyString name, Object& prototype);
     NativeFunction(SafeFunction<ThrowCompletionOr<Value>(VM&)>, Object* prototype, Realm& realm);
-    NativeFunction(FlyString name, SafeFunction<ThrowCompletionOr<Value>(VM&)>, Object& prototype);
+    NativeFunction(DeprecatedFlyString name, SafeFunction<ThrowCompletionOr<Value>(VM&)>, Object& prototype);
     explicit NativeFunction(Object& prototype);
 
 private:
     virtual bool is_native_function() const final { return true; }
 
-    FlyString m_name;
-    Optional<FlyString> m_initial_name; // [[InitialName]]
+    DeprecatedFlyString m_name;
+    Optional<DeprecatedFlyString> m_initial_name; // [[InitialName]]
     SafeFunction<ThrowCompletionOr<Value>(VM&)> m_native_function;
     Realm* m_realm { nullptr };
 };
diff --git a/Userland/Libraries/LibJS/Runtime/Object.cpp b/Userland/Libraries/LibJS/Runtime/Object.cpp
index 3ae26f30909..489a8387338 100644
--- a/Userland/Libraries/LibJS/Runtime/Object.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Object.cpp
@@ -24,7 +24,7 @@
 
 namespace JS {
 
-static HashMap<Object const*, HashMap<FlyString, Object::IntrinsicAccessor>> s_intrinsics;
+static HashMap<Object const*, HashMap<DeprecatedFlyString, Object::IntrinsicAccessor>> s_intrinsics;
 
 // 10.1.12 OrdinaryObjectCreate ( proto [ , additionalInternalSlotsList ] ), https://tc39.es/ecma262/#sec-ordinaryobjectcreate
 NonnullGCPtr<Object> Object::create(Realm& realm, Object* prototype)
@@ -1259,7 +1259,7 @@ Optional<Completion> Object::enumerate_object_properties(Function<Optional<Compl
     //    * Enumerating the properties of the target object includes enumerating properties of its prototype, and the prototype of the prototype, and so on, recursively.
     //    * A property of a prototype is not processed if it has the same name as a property that has already been processed.
 
-    HashTable<FlyString> visited;
+    HashTable<DeprecatedFlyString> visited;
 
     auto const* target = this;
     while (target) {
@@ -1267,7 +1267,7 @@ Optional<Completion> Object::enumerate_object_properties(Function<Optional<Compl
         for (auto& key : own_keys) {
             if (!key.is_string())
                 continue;
-            FlyString property_key = TRY(key.as_string().deprecated_string());
+            DeprecatedFlyString property_key = TRY(key.as_string().deprecated_string());
             if (visited.contains(property_key))
                 continue;
             auto descriptor = TRY(target->internal_get_own_property(property_key));
diff --git a/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.cpp
index 29501bcbe95..cdc4f1e74bf 100644
--- a/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.cpp
@@ -24,7 +24,7 @@ void ObjectEnvironment::visit_edges(Cell::Visitor& visitor)
 }
 
 // 9.1.1.2.1 HasBinding ( N ), https://tc39.es/ecma262/#sec-object-environment-records-hasbinding-n
-ThrowCompletionOr<bool> ObjectEnvironment::has_binding(FlyString const& name, Optional<size_t>*) const
+ThrowCompletionOr<bool> ObjectEnvironment::has_binding(DeprecatedFlyString const& name, Optional<size_t>*) const
 {
     auto& vm = this->vm();
 
@@ -59,7 +59,7 @@ ThrowCompletionOr<bool> ObjectEnvironment::has_binding(FlyString const& name, Op
 }
 
 // 9.1.1.2.2 CreateMutableBinding ( N, D ), https://tc39.es/ecma262/#sec-object-environment-records-createmutablebinding-n-d
-ThrowCompletionOr<void> ObjectEnvironment::create_mutable_binding(VM&, FlyString const& name, bool can_be_deleted)
+ThrowCompletionOr<void> ObjectEnvironment::create_mutable_binding(VM&, DeprecatedFlyString const& name, bool can_be_deleted)
 {
     // 1. Let bindingObject be envRec.[[BindingObject]].
     // 2. Perform ? DefinePropertyOrThrow(bindingObject, N, PropertyDescriptor { [[Value]]: undefined, [[Writable]]: true, [[Enumerable]]: true, [[Configurable]]: D }).
@@ -70,14 +70,14 @@ ThrowCompletionOr<void> ObjectEnvironment::create_mutable_binding(VM&, FlyString
 }
 
 // 9.1.1.2.3 CreateImmutableBinding ( N, S ), https://tc39.es/ecma262/#sec-object-environment-records-createimmutablebinding-n-s
-ThrowCompletionOr<void> ObjectEnvironment::create_immutable_binding(VM&, FlyString const&, bool)
+ThrowCompletionOr<void> ObjectEnvironment::create_immutable_binding(VM&, DeprecatedFlyString const&, bool)
 {
     // "The CreateImmutableBinding concrete method of an object Environment Record is never used within this specification."
     VERIFY_NOT_REACHED();
 }
 
 // 9.1.1.2.4 InitializeBinding ( N, V ), https://tc39.es/ecma262/#sec-object-environment-records-initializebinding-n-v
-ThrowCompletionOr<void> ObjectEnvironment::initialize_binding(VM& vm, FlyString const& name, Value value)
+ThrowCompletionOr<void> ObjectEnvironment::initialize_binding(VM& vm, DeprecatedFlyString const& name, Value value)
 {
     // 1. Perform ? envRec.SetMutableBinding(N, V, false).
     TRY(set_mutable_binding(vm, name, value, false));
@@ -87,7 +87,7 @@ ThrowCompletionOr<void> ObjectEnvironment::initialize_binding(VM& vm, FlyString
 }
 
 // 9.1.1.2.5 SetMutableBinding ( N, V, S ), https://tc39.es/ecma262/#sec-object-environment-records-setmutablebinding-n-v-s
-ThrowCompletionOr<void> ObjectEnvironment::set_mutable_binding(VM&, FlyString const& name, Value value, bool strict)
+ThrowCompletionOr<void> ObjectEnvironment::set_mutable_binding(VM&, DeprecatedFlyString const& name, Value value, bool strict)
 {
     auto& vm = this->vm();
 
@@ -129,7 +129,7 @@ ThrowCompletionOr<void> ObjectEnvironment::set_mutable_binding(VM&, FlyString co
 }
 
 // 9.1.1.2.6 GetBindingValue ( N, S ), https://tc39.es/ecma262/#sec-object-environment-records-getbindingvalue-n-s
-ThrowCompletionOr<Value> ObjectEnvironment::get_binding_value(VM&, FlyString const& name, bool strict)
+ThrowCompletionOr<Value> ObjectEnvironment::get_binding_value(VM&, DeprecatedFlyString const& name, bool strict)
 {
     auto& vm = this->vm();
 
@@ -158,7 +158,7 @@ ThrowCompletionOr<Value> ObjectEnvironment::get_binding_value(VM&, FlyString con
 }
 
 // 9.1.1.2.7 DeleteBinding ( N ), https://tc39.es/ecma262/#sec-object-environment-records-deletebinding-n
-ThrowCompletionOr<bool> ObjectEnvironment::delete_binding(VM&, FlyString const& name)
+ThrowCompletionOr<bool> ObjectEnvironment::delete_binding(VM&, DeprecatedFlyString const& name)
 {
     // 1. Let bindingObject be envRec.[[BindingObject]].
     // 2. Return ? bindingObject.[[Delete]](N).
diff --git a/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.h b/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.h
index 813a711ccd4..bd3bbc7729b 100644
--- a/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/ObjectEnvironment.h
@@ -19,13 +19,13 @@ public:
         Yes,
     };
 
-    virtual ThrowCompletionOr<bool> has_binding(FlyString const& name, Optional<size_t>* = nullptr) const override;
-    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, FlyString const& name, bool can_be_deleted) override;
-    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<void> initialize_binding(VM&, FlyString const& name, Value) override;
-    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, FlyString const& name, Value, bool strict) override;
-    virtual ThrowCompletionOr<Value> get_binding_value(VM&, FlyString const& name, bool strict) override;
-    virtual ThrowCompletionOr<bool> delete_binding(VM&, FlyString const& name) override;
+    virtual ThrowCompletionOr<bool> has_binding(DeprecatedFlyString const& name, Optional<size_t>* = nullptr) const override;
+    virtual ThrowCompletionOr<void> create_mutable_binding(VM&, DeprecatedFlyString const& name, bool can_be_deleted) override;
+    virtual ThrowCompletionOr<void> create_immutable_binding(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<void> initialize_binding(VM&, DeprecatedFlyString const& name, Value) override;
+    virtual ThrowCompletionOr<void> set_mutable_binding(VM&, DeprecatedFlyString const& name, Value, bool strict) override;
+    virtual ThrowCompletionOr<Value> get_binding_value(VM&, DeprecatedFlyString const& name, bool strict) override;
+    virtual ThrowCompletionOr<bool> delete_binding(VM&, DeprecatedFlyString const& name) override;
 
     // 9.1.1.2.10 WithBaseObject ( ), https://tc39.es/ecma262/#sec-object-environment-records-withbaseobject
     virtual Object* with_base_object() const override
diff --git a/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.cpp b/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.cpp
index 8785cea00c3..551508a352d 100644
--- a/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.cpp
+++ b/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.cpp
@@ -19,7 +19,7 @@ PrivateEnvironment::PrivateEnvironment(PrivateEnvironment* parent)
 // Note: we start at one such that 0 can be invalid / default initialized.
 u64 PrivateEnvironment::s_next_id = 1u;
 
-PrivateName PrivateEnvironment::resolve_private_identifier(FlyString const& identifier) const
+PrivateName PrivateEnvironment::resolve_private_identifier(DeprecatedFlyString const& identifier) const
 {
     auto name_or_end = find_private_name(identifier);
 
@@ -32,7 +32,7 @@ PrivateName PrivateEnvironment::resolve_private_identifier(FlyString const& iden
     return m_outer_environment->resolve_private_identifier(identifier);
 }
 
-void PrivateEnvironment::add_private_name(Badge<ClassExpression>, FlyString description)
+void PrivateEnvironment::add_private_name(Badge<ClassExpression>, DeprecatedFlyString description)
 {
     if (!find_private_name(description).is_end())
         return;
diff --git a/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.h b/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.h
index f9c6d07b052..055b5b5e808 100644
--- a/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.h
+++ b/Userland/Libraries/LibJS/Runtime/PrivateEnvironment.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/StringView.h>
 #include <AK/Vector.h>
 #include <LibJS/Heap/Cell.h>
@@ -15,14 +15,14 @@ namespace JS {
 
 struct PrivateName {
     PrivateName() = default;
-    PrivateName(u64 unique_id, FlyString description)
+    PrivateName(u64 unique_id, DeprecatedFlyString description)
         : unique_id(unique_id)
         , description(move(description))
     {
     }
 
     u64 unique_id { 0 };
-    FlyString description;
+    DeprecatedFlyString description;
 
     bool operator==(PrivateName const& rhs) const;
 };
@@ -31,16 +31,16 @@ class PrivateEnvironment : public Cell {
     JS_CELL(PrivateEnvironment, Cell);
 
 public:
-    PrivateName resolve_private_identifier(FlyString const& identifier) const;
+    PrivateName resolve_private_identifier(DeprecatedFlyString const& identifier) const;
 
-    void add_private_name(Badge<ClassExpression>, FlyString description);
+    void add_private_name(Badge<ClassExpression>, DeprecatedFlyString description);
 
 private:
     explicit PrivateEnvironment(PrivateEnvironment* parent);
 
     virtual void visit_edges(Visitor&) override;
 
-    auto find_private_name(FlyString const& description) const
+    auto find_private_name(DeprecatedFlyString const& description) const
     {
         return m_private_names.find_if([&](PrivateName const& private_name) {
             return private_name.description == description;
diff --git a/Userland/Libraries/LibJS/Runtime/PropertyKey.h b/Userland/Libraries/LibJS/Runtime/PropertyKey.h
index 34cd41f4fe4..e88bbb1e90d 100644
--- a/Userland/Libraries/LibJS/Runtime/PropertyKey.h
+++ b/Userland/Libraries/LibJS/Runtime/PropertyKey.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Heap/Handle.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/StringOrSymbol.h>
@@ -61,18 +61,18 @@ public:
 
     PropertyKey(char const* chars)
         : m_type(Type::String)
-        , m_string(FlyString(chars))
+        , m_string(DeprecatedFlyString(chars))
     {
     }
 
     PropertyKey(DeprecatedString const& string)
         : m_type(Type::String)
-        , m_string(FlyString(string))
+        , m_string(DeprecatedFlyString(string))
     {
         VERIFY(!m_string.is_null());
     }
 
-    PropertyKey(FlyString string, StringMayBeNumber string_may_be_number = StringMayBeNumber::Yes)
+    PropertyKey(DeprecatedFlyString string, StringMayBeNumber string_may_be_number = StringMayBeNumber::Yes)
         : m_string_may_be_number(string_may_be_number == StringMayBeNumber::Yes)
         , m_type(Type::String)
         , m_string(move(string))
@@ -152,7 +152,7 @@ public:
         return m_number;
     }
 
-    FlyString const& as_string() const
+    DeprecatedFlyString const& as_string() const
     {
         VERIFY(is_string());
         return m_string;
@@ -186,7 +186,7 @@ private:
     bool m_string_may_be_number { true };
     Type m_type { Type::Invalid };
     u32 m_number { 0 };
-    FlyString m_string;
+    DeprecatedFlyString m_string;
     Handle<Symbol> m_symbol;
 };
 
diff --git a/Userland/Libraries/LibJS/Runtime/ProxyObject.cpp b/Userland/Libraries/LibJS/Runtime/ProxyObject.cpp
index 5d883a1c924..a71a76d8a35 100644
--- a/Userland/Libraries/LibJS/Runtime/ProxyObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ProxyObject.cpp
@@ -832,7 +832,7 @@ void ProxyObject::visit_edges(Cell::Visitor& visitor)
     visitor.visit(&m_handler);
 }
 
-FlyString const& ProxyObject::name() const
+DeprecatedFlyString const& ProxyObject::name() const
 {
     VERIFY(is_function());
     return static_cast<FunctionObject&>(m_target).name();
diff --git a/Userland/Libraries/LibJS/Runtime/ProxyObject.h b/Userland/Libraries/LibJS/Runtime/ProxyObject.h
index 7aa955e26d8..7d5cba3346f 100644
--- a/Userland/Libraries/LibJS/Runtime/ProxyObject.h
+++ b/Userland/Libraries/LibJS/Runtime/ProxyObject.h
@@ -20,7 +20,7 @@ public:
 
     virtual ~ProxyObject() override = default;
 
-    virtual FlyString const& name() const override;
+    virtual DeprecatedFlyString const& name() const override;
     virtual bool has_constructor() const override;
 
     Object const& target() const { return m_target; }
diff --git a/Userland/Libraries/LibJS/Runtime/Reference.cpp b/Userland/Libraries/LibJS/Runtime/Reference.cpp
index 21af7d06b45..06a16337a21 100644
--- a/Userland/Libraries/LibJS/Runtime/Reference.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Reference.cpp
@@ -239,7 +239,7 @@ ThrowCompletionOr<void> Reference::initialize_referenced_binding(VM& vm, Value v
 }
 
 // 6.2.4.9 MakePrivateReference ( baseValue, privateIdentifier ), https://tc39.es/ecma262/#sec-makeprivatereference
-Reference make_private_reference(VM& vm, Value base_value, FlyString const& private_identifier)
+Reference make_private_reference(VM& vm, Value base_value, DeprecatedFlyString const& private_identifier)
 {
     // 1. Let privEnv be the running execution context's PrivateEnvironment.
     auto* private_environment = vm.running_execution_context().private_environment;
diff --git a/Userland/Libraries/LibJS/Runtime/Reference.h b/Userland/Libraries/LibJS/Runtime/Reference.h
index 10c19fc04b6..f0d716b2963 100644
--- a/Userland/Libraries/LibJS/Runtime/Reference.h
+++ b/Userland/Libraries/LibJS/Runtime/Reference.h
@@ -14,7 +14,7 @@
 
 namespace JS {
 
-Reference make_private_reference(VM&, Value base_value, FlyString const& private_identifier);
+Reference make_private_reference(VM&, Value base_value, DeprecatedFlyString const& private_identifier);
 
 class Reference {
 public:
@@ -47,7 +47,7 @@ public:
         }
     }
 
-    Reference(Environment& base, FlyString referenced_name, bool strict = false, Optional<EnvironmentCoordinate> environment_coordinate = {})
+    Reference(Environment& base, DeprecatedFlyString referenced_name, bool strict = false, Optional<EnvironmentCoordinate> environment_coordinate = {})
         : m_base_type(BaseType::Environment)
         , m_base_environment(&base)
         , m_name(move(referenced_name))
diff --git a/Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp b/Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp
index 0b056697d32..e1dd4cb73bb 100644
--- a/Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp
@@ -95,7 +95,7 @@ static Value get_match_index_par(VM& vm, Utf16View const& string, Match const& m
 }
 
 // 22.2.5.2.8 MakeMatchIndicesIndexPairArray ( S, indices, groupNames, hasGroups ), https://tc39.es/ecma262/#sec-makematchindicesindexpairarray
-static Value make_match_indices_index_pair_array(VM& vm, Utf16View const& string, Vector<Optional<Match>> const& indices, HashMap<FlyString, Match> const& group_names, bool has_groups)
+static Value make_match_indices_index_pair_array(VM& vm, Utf16View const& string, Vector<Optional<Match>> const& indices, HashMap<DeprecatedFlyString, Match> const& group_names, bool has_groups)
 {
     // Note: This implementation differs from the spec, but has the same behavior.
     //
@@ -268,7 +268,7 @@ static ThrowCompletionOr<Value> regexp_builtin_exec(VM& vm, RegExpObject& regexp
     Vector<Utf16String> captured_values;
 
     // 25. Let groupNames be a new empty List.
-    HashMap<FlyString, Match> group_names;
+    HashMap<DeprecatedFlyString, Match> group_names;
 
     // 26. Add match as the last element of indices.
     indices.append(move(match_indices));
diff --git a/Userland/Libraries/LibJS/Runtime/StringOrSymbol.h b/Userland/Libraries/LibJS/Runtime/StringOrSymbol.h
index 1da6be44df4..c58076d0819 100644
--- a/Userland/Libraries/LibJS/Runtime/StringOrSymbol.h
+++ b/Userland/Libraries/LibJS/Runtime/StringOrSymbol.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Runtime/PrimitiveString.h>
 #include <LibJS/Runtime/Symbol.h>
 #include <LibJS/Runtime/Value.h>
@@ -18,16 +18,16 @@ public:
     StringOrSymbol() = default;
 
     StringOrSymbol(char const* chars)
-        : StringOrSymbol(FlyString(chars))
+        : StringOrSymbol(DeprecatedFlyString(chars))
     {
     }
 
     StringOrSymbol(DeprecatedString const& string)
-        : StringOrSymbol(FlyString(string))
+        : StringOrSymbol(DeprecatedFlyString(string))
     {
     }
 
-    StringOrSymbol(FlyString const& string)
+    StringOrSymbol(DeprecatedFlyString const& string)
         : m_ptr(string.impl())
     {
         VERIFY(!string.is_null());
@@ -62,10 +62,10 @@ public:
     ALWAYS_INLINE bool is_symbol() const { return is_valid() && (bits() & 1ul); }
     ALWAYS_INLINE bool is_string() const { return is_valid() && !(bits() & 1ul); }
 
-    ALWAYS_INLINE FlyString as_string() const
+    ALWAYS_INLINE DeprecatedFlyString as_string() const
     {
         VERIFY(is_string());
-        return FlyString::from_fly_impl(as_string_impl());
+        return DeprecatedFlyString::from_fly_impl(as_string_impl());
     }
 
     ALWAYS_INLINE Symbol const* as_symbol() const
diff --git a/Userland/Libraries/LibJS/Runtime/TypedArray.cpp b/Userland/Libraries/LibJS/Runtime/TypedArray.cpp
index 9ecad32e6df..b1ef270f05d 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArray.cpp
+++ b/Userland/Libraries/LibJS/Runtime/TypedArray.cpp
@@ -453,7 +453,7 @@ void TypedArrayBase::visit_edges(Visitor& visitor)
     {                                                                                                                            \
     }                                                                                                                            \
                                                                                                                                  \
-    FlyString const& ClassName::element_name() const                                                                             \
+    DeprecatedFlyString const& ClassName::element_name() const                                                                   \
     {                                                                                                                            \
         return vm().names.ClassName.as_string();                                                                                 \
     }                                                                                                                            \
diff --git a/Userland/Libraries/LibJS/Runtime/TypedArray.h b/Userland/Libraries/LibJS/Runtime/TypedArray.h
index d4701df3ee9..7096bfc019f 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArray.h
+++ b/Userland/Libraries/LibJS/Runtime/TypedArray.h
@@ -47,7 +47,7 @@ public:
     void set_viewed_array_buffer(ArrayBuffer* array_buffer) { m_viewed_array_buffer = array_buffer; }
 
     virtual size_t element_size() const = 0;
-    virtual FlyString const& element_name() const = 0;
+    virtual DeprecatedFlyString const& element_name() const = 0;
 
     // 25.1.2.6 IsUnclampedIntegerElementType ( type ), https://tc39.es/ecma262/#sec-isunclampedintegerelementtype
     virtual bool is_unclamped_integer_element_type() const = 0;
@@ -470,7 +470,7 @@ ThrowCompletionOr<double> compare_typed_array_elements(VM&, Value x, Value y, Fu
         static ThrowCompletionOr<NonnullGCPtr<ClassName>> create(Realm&, u32 length, FunctionObject& new_target); \
         static ThrowCompletionOr<NonnullGCPtr<ClassName>> create(Realm&, u32 length);                             \
         static NonnullGCPtr<ClassName> create(Realm&, u32 length, ArrayBuffer& buffer);                           \
-        virtual FlyString const& element_name() const override;                                                   \
+        virtual DeprecatedFlyString const& element_name() const override;                                         \
                                                                                                                   \
     protected:                                                                                                    \
         ClassName(Object& prototype, u32 length, ArrayBuffer& array_buffer);                                      \
diff --git a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
index 4e0bf473767..14748455d06 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
+++ b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.cpp
@@ -11,7 +11,7 @@
 
 namespace JS {
 
-TypedArrayConstructor::TypedArrayConstructor(FlyString const& name, Object& prototype)
+TypedArrayConstructor::TypedArrayConstructor(DeprecatedFlyString const& name, Object& prototype)
     : NativeFunction(name, prototype)
 {
 }
diff --git a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
index c4c66209e4e..3d9ae5a08e7 100644
--- a/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
+++ b/Userland/Libraries/LibJS/Runtime/TypedArrayConstructor.h
@@ -22,7 +22,7 @@ public:
     virtual ThrowCompletionOr<NonnullGCPtr<Object>> construct(FunctionObject& new_target) override;
 
 protected:
-    TypedArrayConstructor(FlyString const& name, Object& prototype);
+    TypedArrayConstructor(DeprecatedFlyString const& name, Object& prototype);
 
 private:
     virtual bool has_constructor() const override { return true; }
diff --git a/Userland/Libraries/LibJS/Runtime/VM.cpp b/Userland/Libraries/LibJS/Runtime/VM.cpp
index c325456d64c..836c9bfb883 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.cpp
+++ b/Userland/Libraries/LibJS/Runtime/VM.cpp
@@ -231,7 +231,7 @@ void VM::gather_roots(HashTable<Cell*>& roots)
         roots.set(finalization_registry);
 }
 
-ThrowCompletionOr<Value> VM::named_evaluation_if_anonymous_function(ASTNode const& expression, FlyString const& name)
+ThrowCompletionOr<Value> VM::named_evaluation_if_anonymous_function(ASTNode const& expression, DeprecatedFlyString const& name)
 {
     // 8.3.3 Static Semantics: IsAnonymousFunctionDefinition ( expr ), https://tc39.es/ecma262/#sec-isanonymousfunctiondefinition
     // And 8.3.5 Runtime Semantics: NamedEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-namedevaluation
@@ -260,7 +260,7 @@ ThrowCompletionOr<void> VM::destructuring_assignment_evaluation(NonnullRefPtr<Bi
 }
 
 // 8.5.2 Runtime Semantics: BindingInitialization, https://tc39.es/ecma262/#sec-runtime-semantics-bindinginitialization
-ThrowCompletionOr<void> VM::binding_initialization(FlyString const& target, Value value, Environment* environment)
+ThrowCompletionOr<void> VM::binding_initialization(DeprecatedFlyString const& target, Value value, Environment* environment)
 {
     // 1. Let name be StringValue of Identifier.
     // 2. Return ? InitializeBoundName(name, value, environment).
@@ -541,7 +541,7 @@ ThrowCompletionOr<void> VM::iterator_binding_initialization(BindingPattern const
 }
 
 // 9.1.2.1 GetIdentifierReference ( env, name, strict ), https://tc39.es/ecma262/#sec-getidentifierreference
-ThrowCompletionOr<Reference> VM::get_identifier_reference(Environment* environment, FlyString name, bool strict, size_t hops)
+ThrowCompletionOr<Reference> VM::get_identifier_reference(Environment* environment, DeprecatedFlyString name, bool strict, size_t hops)
 {
     // 1. If env is the value null, then
     if (!environment) {
@@ -575,7 +575,7 @@ ThrowCompletionOr<Reference> VM::get_identifier_reference(Environment* environme
 }
 
 // 9.4.2 ResolveBinding ( name [ , env ] ), https://tc39.es/ecma262/#sec-resolvebinding
-ThrowCompletionOr<Reference> VM::resolve_binding(FlyString const& name, Environment* environment)
+ThrowCompletionOr<Reference> VM::resolve_binding(DeprecatedFlyString const& name, Environment* environment)
 {
     // 1. If env is not present or if env is undefined, then
     if (!environment) {
diff --git a/Userland/Libraries/LibJS/Runtime/VM.h b/Userland/Libraries/LibJS/Runtime/VM.h
index e22a90f649d..7ff9087d10d 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.h
+++ b/Userland/Libraries/LibJS/Runtime/VM.h
@@ -8,7 +8,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/RefCounted.h>
@@ -175,8 +175,8 @@ public:
     u32 execution_generation() const { return m_execution_generation; }
     void finish_execution_generation() { ++m_execution_generation; }
 
-    ThrowCompletionOr<Reference> resolve_binding(FlyString const&, Environment* = nullptr);
-    ThrowCompletionOr<Reference> get_identifier_reference(Environment*, FlyString, bool strict, size_t hops = 0);
+    ThrowCompletionOr<Reference> resolve_binding(DeprecatedFlyString const&, Environment* = nullptr);
+    ThrowCompletionOr<Reference> get_identifier_reference(Environment*, DeprecatedFlyString, bool strict, size_t hops = 0);
 
     // 5.2.3.2 Throw an Exception, https://tc39.es/ecma262/#sec-throw-an-exception
     template<typename T, typename... Args>
@@ -213,10 +213,10 @@ public:
     CustomData* custom_data() { return m_custom_data; }
 
     ThrowCompletionOr<void> destructuring_assignment_evaluation(NonnullRefPtr<BindingPattern> const& target, Value value);
-    ThrowCompletionOr<void> binding_initialization(FlyString const& target, Value value, Environment* environment);
+    ThrowCompletionOr<void> binding_initialization(DeprecatedFlyString const& target, Value value, Environment* environment);
     ThrowCompletionOr<void> binding_initialization(NonnullRefPtr<BindingPattern> const& target, Value value, Environment* environment);
 
-    ThrowCompletionOr<Value> named_evaluation_if_anonymous_function(ASTNode const& expression, FlyString const& name);
+    ThrowCompletionOr<Value> named_evaluation_if_anonymous_function(ASTNode const& expression, DeprecatedFlyString const& name);
 
     void save_execution_context_stack();
     void restore_execution_context_stack();
diff --git a/Userland/Libraries/LibJS/Runtime/WrappedFunction.h b/Userland/Libraries/LibJS/Runtime/WrappedFunction.h
index 555835327d9..9d8e67bb636 100644
--- a/Userland/Libraries/LibJS/Runtime/WrappedFunction.h
+++ b/Userland/Libraries/LibJS/Runtime/WrappedFunction.h
@@ -22,7 +22,7 @@ public:
     virtual ThrowCompletionOr<Value> internal_call(Value this_argument, MarkedVector<Value> arguments_list) override;
 
     // FIXME: Remove this (and stop inventing random internal slots that shouldn't exist, jeez)
-    virtual FlyString const& name() const override { return m_wrapped_target_function.name(); }
+    virtual DeprecatedFlyString const& name() const override { return m_wrapped_target_function.name(); }
 
     virtual Realm* realm() const override { return &m_realm; }
 
diff --git a/Userland/Libraries/LibJS/SourceTextModule.cpp b/Userland/Libraries/LibJS/SourceTextModule.cpp
index ca4c2c8d2dc..2664002911f 100644
--- a/Userland/Libraries/LibJS/SourceTextModule.cpp
+++ b/Userland/Libraries/LibJS/SourceTextModule.cpp
@@ -260,7 +260,7 @@ Result<NonnullGCPtr<SourceTextModule>, Vector<ParserError>> SourceTextModule::pa
 }
 
 // 16.2.1.6.2 GetExportedNames ( [ exportStarSet ] ), https://tc39.es/ecma262/#sec-getexportednames
-ThrowCompletionOr<Vector<FlyString>> SourceTextModule::get_exported_names(VM& vm, Vector<Module*> export_star_set)
+ThrowCompletionOr<Vector<DeprecatedFlyString>> SourceTextModule::get_exported_names(VM& vm, Vector<Module*> export_star_set)
 {
     dbgln_if(JS_MODULE_DEBUG, "[JS MODULE] get_export_names of {}", filename());
     // 1. If exportStarSet is not present, set exportStarSet to a new empty List.
@@ -272,14 +272,14 @@ ThrowCompletionOr<Vector<FlyString>> SourceTextModule::get_exported_names(VM& vm
         // FIXME: How do we check that?
 
         // b. Return a new empty List.
-        return Vector<FlyString> {};
+        return Vector<DeprecatedFlyString> {};
     }
 
     // 3. Append module to exportStarSet.
     export_star_set.append(this);
 
     // 4. Let exportedNames be a new empty List.
-    Vector<FlyString> exported_names;
+    Vector<DeprecatedFlyString> exported_names;
 
     // 5. For each ExportEntry Record e of module.[[LocalExportEntries]], do
     for (auto& entry : m_local_export_entries) {
@@ -432,7 +432,7 @@ ThrowCompletionOr<void> SourceTextModule::initialize_environment(VM& vm)
     // Note: We just loop through them in step 21.
 
     // 20. Let declaredVarNames be a new empty List.
-    Vector<FlyString> declared_var_names;
+    Vector<DeprecatedFlyString> declared_var_names;
 
     // 21. For each element d of varDeclarations, do
     // a. For each element dn of the BoundNames of d, do
@@ -459,7 +459,7 @@ ThrowCompletionOr<void> SourceTextModule::initialize_environment(VM& vm)
     // 24. For each element d of lexDeclarations, do
     m_ecmascript_code->for_each_lexically_scoped_declaration([&](Declaration const& declaration) {
         // a. For each element dn of the BoundNames of d, do
-        declaration.for_each_bound_name([&](FlyString const& name) {
+        declaration.for_each_bound_name([&](DeprecatedFlyString const& name) {
             // i. If IsConstantDeclaration of d is true, then
             if (declaration.is_constant_declaration()) {
                 // 1. Perform ! env.CreateImmutableBinding(dn, true).
@@ -479,7 +479,7 @@ ThrowCompletionOr<void> SourceTextModule::initialize_environment(VM& vm)
                 // 1. Let fo be InstantiateFunctionObject of d with arguments env and privateEnv.
                 // NOTE: Special case if the function is a default export of an anonymous function
                 //       it has name "*default*" but internally should have name "default".
-                FlyString function_name = function_declaration.name();
+                DeprecatedFlyString function_name = function_declaration.name();
                 if (function_name == ExportStatement::local_name_for_default)
                     function_name = "default"sv;
                 auto function = ECMAScriptFunctionObject::create(realm(), function_name, function_declaration.source_text(), function_declaration.body(), function_declaration.parameters(), function_declaration.function_length(), environment, private_environment, function_declaration.kind(), function_declaration.is_strict_mode(), function_declaration.might_need_arguments_object(), function_declaration.contains_direct_call_to_eval());
@@ -518,7 +518,7 @@ ThrowCompletionOr<void> SourceTextModule::initialize_environment(VM& vm)
 }
 
 // 16.2.1.6.3 ResolveExport ( exportName [ , resolveSet ] ), https://tc39.es/ecma262/#sec-resolveexport
-ThrowCompletionOr<ResolvedBinding> SourceTextModule::resolve_export(VM& vm, FlyString const& export_name, Vector<ResolvedBinding> resolve_set)
+ThrowCompletionOr<ResolvedBinding> SourceTextModule::resolve_export(VM& vm, DeprecatedFlyString const& export_name, Vector<ResolvedBinding> resolve_set)
 {
     // 1. If resolveSet is not present, set resolveSet to a new empty List.
     // Note: This is done by the default argument.
diff --git a/Userland/Libraries/LibJS/SourceTextModule.h b/Userland/Libraries/LibJS/SourceTextModule.h
index a6720412801..28dea01f9b7 100644
--- a/Userland/Libraries/LibJS/SourceTextModule.h
+++ b/Userland/Libraries/LibJS/SourceTextModule.h
@@ -22,8 +22,8 @@ public:
 
     Program const& parse_node() const { return *m_ecmascript_code; }
 
-    virtual ThrowCompletionOr<Vector<FlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set) override;
-    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, FlyString const& export_name, Vector<ResolvedBinding> resolve_set = {}) override;
+    virtual ThrowCompletionOr<Vector<DeprecatedFlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set) override;
+    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, DeprecatedFlyString const& export_name, Vector<ResolvedBinding> resolve_set = {}) override;
 
     Object* import_meta() { return m_import_meta; }
     void set_import_meta(Badge<MetaProperty>, Object* import_meta) { m_import_meta = import_meta; }
diff --git a/Userland/Libraries/LibJS/SyntheticModule.cpp b/Userland/Libraries/LibJS/SyntheticModule.cpp
index eb0fdbfeaaf..7e94f5a8a61 100644
--- a/Userland/Libraries/LibJS/SyntheticModule.cpp
+++ b/Userland/Libraries/LibJS/SyntheticModule.cpp
@@ -14,7 +14,7 @@
 namespace JS {
 
 // 1.2.1 CreateSyntheticModule ( exportNames, evaluationSteps, realm, hostDefined ), https://tc39.es/proposal-json-modules/#sec-createsyntheticmodule
-SyntheticModule::SyntheticModule(Vector<FlyString> export_names, SyntheticModule::EvaluationFunction evaluation_steps, Realm& realm, StringView filename)
+SyntheticModule::SyntheticModule(Vector<DeprecatedFlyString> export_names, SyntheticModule::EvaluationFunction evaluation_steps, Realm& realm, StringView filename)
     : Module(realm, filename)
     , m_export_names(move(export_names))
     , m_evaluation_steps(move(evaluation_steps))
@@ -23,14 +23,14 @@ SyntheticModule::SyntheticModule(Vector<FlyString> export_names, SyntheticModule
 }
 
 // 1.2.3.1 GetExportedNames( exportStarSet ), https://tc39.es/proposal-json-modules/#sec-smr-getexportednames
-ThrowCompletionOr<Vector<FlyString>> SyntheticModule::get_exported_names(VM&, Vector<Module*>)
+ThrowCompletionOr<Vector<DeprecatedFlyString>> SyntheticModule::get_exported_names(VM&, Vector<Module*>)
 {
     // 1. Return module.[[ExportNames]].
     return m_export_names;
 }
 
 // 1.2.3.2 ResolveExport( exportName, resolveSet ), https://tc39.es/proposal-json-modules/#sec-smr-resolveexport
-ThrowCompletionOr<ResolvedBinding> SyntheticModule::resolve_export(VM&, FlyString const& export_name, Vector<ResolvedBinding>)
+ThrowCompletionOr<ResolvedBinding> SyntheticModule::resolve_export(VM&, DeprecatedFlyString const& export_name, Vector<ResolvedBinding>)
 {
     // 1. If module.[[ExportNames]] does not contain exportName, return null.
     if (!m_export_names.contains_slow(export_name))
@@ -119,7 +119,7 @@ ThrowCompletionOr<Promise*> SyntheticModule::evaluate(VM& vm)
 }
 
 // 1.2.2 SetSyntheticModuleExport ( module, exportName, exportValue ), https://tc39.es/proposal-json-modules/#sec-setsyntheticmoduleexport
-ThrowCompletionOr<void> SyntheticModule::set_synthetic_module_export(FlyString const& export_name, Value export_value)
+ThrowCompletionOr<void> SyntheticModule::set_synthetic_module_export(DeprecatedFlyString const& export_name, Value export_value)
 {
     auto& vm = this->realm().vm();
 
@@ -139,7 +139,7 @@ NonnullGCPtr<SyntheticModule> SyntheticModule::create_default_export_synthetic_m
     };
 
     // 2. Return CreateSyntheticModule("default", closure, realm)
-    return realm.heap().allocate_without_realm<SyntheticModule>(Vector<FlyString> { "default" }, move(closure), realm, filename);
+    return realm.heap().allocate_without_realm<SyntheticModule>(Vector<DeprecatedFlyString> { "default" }, move(closure), realm, filename);
 }
 
 // 1.4 ParseJSONModule ( source ), https://tc39.es/proposal-json-modules/#sec-parse-json-module
diff --git a/Userland/Libraries/LibJS/SyntheticModule.h b/Userland/Libraries/LibJS/SyntheticModule.h
index 94e5b8be3a5..18f4ea20842 100644
--- a/Userland/Libraries/LibJS/SyntheticModule.h
+++ b/Userland/Libraries/LibJS/SyntheticModule.h
@@ -19,18 +19,18 @@ public:
 
     static NonnullGCPtr<SyntheticModule> create_default_export_synthetic_module(Value default_export, Realm& realm, StringView filename);
 
-    ThrowCompletionOr<void> set_synthetic_module_export(FlyString const& export_name, Value export_value);
+    ThrowCompletionOr<void> set_synthetic_module_export(DeprecatedFlyString const& export_name, Value export_value);
 
     virtual ThrowCompletionOr<void> link(VM& vm) override;
     virtual ThrowCompletionOr<Promise*> evaluate(VM& vm) override;
-    virtual ThrowCompletionOr<Vector<FlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set) override;
-    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, FlyString const& export_name, Vector<ResolvedBinding> resolve_set) override;
+    virtual ThrowCompletionOr<Vector<DeprecatedFlyString>> get_exported_names(VM& vm, Vector<Module*> export_star_set) override;
+    virtual ThrowCompletionOr<ResolvedBinding> resolve_export(VM& vm, DeprecatedFlyString const& export_name, Vector<ResolvedBinding> resolve_set) override;
 
 private:
-    SyntheticModule(Vector<FlyString> export_names, EvaluationFunction evaluation_steps, Realm& realm, StringView filename);
+    SyntheticModule(Vector<DeprecatedFlyString> export_names, EvaluationFunction evaluation_steps, Realm& realm, StringView filename);
 
-    Vector<FlyString> m_export_names;      // [[ExportNames]]
-    EvaluationFunction m_evaluation_steps; // [[EvaluationSteps]]
+    Vector<DeprecatedFlyString> m_export_names; // [[ExportNames]]
+    EvaluationFunction m_evaluation_steps;      // [[EvaluationSteps]]
 };
 
 ThrowCompletionOr<NonnullGCPtr<Module>> parse_json_module(StringView source_text, Realm& realm, StringView filename);
diff --git a/Userland/Libraries/LibJS/Token.h b/Userland/Libraries/LibJS/Token.h
index aa2f8083e56..9ebc6c2f233 100644
--- a/Userland/Libraries/LibJS/Token.h
+++ b/Userland/Libraries/LibJS/Token.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/StringView.h>
 #include <AK/Variant.h>
 
@@ -207,16 +207,16 @@ public:
     {
         return m_value.visit(
             [](StringView view) { return view; },
-            [](FlyString const& identifier) { return identifier.view(); },
+            [](DeprecatedFlyString const& identifier) { return identifier.view(); },
             [](Empty) -> StringView { VERIFY_NOT_REACHED(); });
     }
 
-    FlyString flystring_value() const
+    DeprecatedFlyString DeprecatedFlyString_value() const
     {
         return m_value.visit(
-            [](StringView view) -> FlyString { return view; },
-            [](FlyString const& identifier) -> FlyString { return identifier; },
-            [](Empty) -> FlyString { VERIFY_NOT_REACHED(); });
+            [](StringView view) -> DeprecatedFlyString { return view; },
+            [](DeprecatedFlyString const& identifier) -> DeprecatedFlyString { return identifier; },
+            [](Empty) -> DeprecatedFlyString { VERIFY_NOT_REACHED(); });
     }
 
     StringView filename() const { return m_filename; }
@@ -236,7 +236,7 @@ public:
     DeprecatedString string_value(StringValueStatus& status) const;
     DeprecatedString raw_template_value() const;
 
-    void set_identifier_value(FlyString value)
+    void set_identifier_value(DeprecatedFlyString value)
     {
         m_value = move(value);
     }
@@ -249,7 +249,7 @@ private:
     DeprecatedString m_message;
     StringView m_trivia;
     StringView m_original_value;
-    Variant<Empty, StringView, FlyString> m_value {};
+    Variant<Empty, StringView, DeprecatedFlyString> m_value {};
     StringView m_filename;
     size_t m_line_number { 0 };
     size_t m_line_column { 0 };
diff --git a/Userland/Libraries/LibPDF/ColorSpace.cpp b/Userland/Libraries/LibPDF/ColorSpace.cpp
index 47ffbf181c1..5fbdfddb5d1 100644
--- a/Userland/Libraries/LibPDF/ColorSpace.cpp
+++ b/Userland/Libraries/LibPDF/ColorSpace.cpp
@@ -16,7 +16,7 @@ namespace PDF {
 ENUMERATE_COLOR_SPACE_FAMILIES(ENUMERATE);
 #undef ENUMERATE
 
-PDFErrorOr<ColorSpaceFamily> ColorSpaceFamily::get(FlyString const& family_name)
+PDFErrorOr<ColorSpaceFamily> ColorSpaceFamily::get(DeprecatedFlyString const& family_name)
 {
 #define ENUMERATE(f_name, ever_needs_parameters) \
     if (family_name == f_name.name()) {          \
@@ -27,7 +27,7 @@ PDFErrorOr<ColorSpaceFamily> ColorSpaceFamily::get(FlyString const& family_name)
     return Error(Error::Type::MalformedPDF, DeprecatedString::formatted("Unknown ColorSpace family {}", family_name));
 }
 
-PDFErrorOr<NonnullRefPtr<ColorSpace>> ColorSpace::create(FlyString const& name)
+PDFErrorOr<NonnullRefPtr<ColorSpace>> ColorSpace::create(DeprecatedFlyString const& name)
 {
     // Simple color spaces with no parameters, which can be specified directly
     if (name == CommonNames::DeviceGray)
@@ -305,7 +305,7 @@ PDFErrorOr<NonnullRefPtr<ColorSpace>> ICCBasedColorSpace::create(Document* docum
 
     auto dict = param.get<NonnullRefPtr<Object>>()->cast<StreamObject>()->dict();
 
-    FlyString name;
+    DeprecatedFlyString name;
     if (!dict->contains(CommonNames::Alternate)) {
         auto number_of_components = dict->get_value(CommonNames::N).to_int();
         if (number_of_components == 1)
diff --git a/Userland/Libraries/LibPDF/ColorSpace.h b/Userland/Libraries/LibPDF/ColorSpace.h
index 9ff28aa0f1d..bbffb3db577 100644
--- a/Userland/Libraries/LibPDF/ColorSpace.h
+++ b/Userland/Libraries/LibPDF/ColorSpace.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Forward.h>
 #include <LibGfx/Color.h>
 #include <LibPDF/Value.h>
@@ -28,28 +28,28 @@ namespace PDF {
 
 class ColorSpaceFamily {
 public:
-    ColorSpaceFamily(FlyString name, bool never_needs_paramaters_p)
+    ColorSpaceFamily(DeprecatedFlyString name, bool never_needs_paramaters_p)
         : m_name(move(name))
         , m_never_needs_parameters(never_needs_paramaters_p)
     {
     }
 
-    FlyString name() const { return m_name; };
+    DeprecatedFlyString name() const { return m_name; };
     bool never_needs_parameters() const { return m_never_needs_parameters; };
-    static PDFErrorOr<ColorSpaceFamily> get(FlyString const&);
+    static PDFErrorOr<ColorSpaceFamily> get(DeprecatedFlyString const&);
 
 #define ENUMERATE(name, ever_needs_parameters) static ColorSpaceFamily name;
     ENUMERATE_COLOR_SPACE_FAMILIES(ENUMERATE)
 #undef ENUMERATE
 
 private:
-    FlyString m_name;
+    DeprecatedFlyString m_name;
     bool m_never_needs_parameters;
 };
 
 class ColorSpace : public RefCounted<ColorSpace> {
 public:
-    static PDFErrorOr<NonnullRefPtr<ColorSpace>> create(FlyString const&);
+    static PDFErrorOr<NonnullRefPtr<ColorSpace>> create(DeprecatedFlyString const&);
     static PDFErrorOr<NonnullRefPtr<ColorSpace>> create(Document*, NonnullRefPtr<ArrayObject>);
 
     virtual ~ColorSpace() = default;
diff --git a/Userland/Libraries/LibPDF/CommonNames.cpp b/Userland/Libraries/LibPDF/CommonNames.cpp
index 015f9ac932e..f0ac03a0ca5 100644
--- a/Userland/Libraries/LibPDF/CommonNames.cpp
+++ b/Userland/Libraries/LibPDF/CommonNames.cpp
@@ -8,10 +8,10 @@
 
 namespace PDF {
 
-#define ENUMERATE(name) FlyString CommonNames::name = #name;
+#define ENUMERATE(name) DeprecatedFlyString CommonNames::name = #name;
 ENUMERATE_COMMON_NAMES(ENUMERATE)
 #undef ENUMERATE
 
-FlyString CommonNames::IdentityH = "Identity-H";
+DeprecatedFlyString CommonNames::IdentityH = "Identity-H";
 
 }
diff --git a/Userland/Libraries/LibPDF/CommonNames.h b/Userland/Libraries/LibPDF/CommonNames.h
index a3832ba2b3f..907f3ff5245 100644
--- a/Userland/Libraries/LibPDF/CommonNames.h
+++ b/Userland/Libraries/LibPDF/CommonNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 #define ENUMERATE_COMMON_NAMES(A) \
     A(AIS)                        \
@@ -150,11 +150,11 @@ namespace PDF {
 
 class CommonNames {
 public:
-#define ENUMERATE(name) static FlyString name;
+#define ENUMERATE(name) static DeprecatedFlyString name;
     ENUMERATE_COMMON_NAMES(ENUMERATE)
 #undef ENUMERATE
 
-    static FlyString IdentityH;
+    static DeprecatedFlyString IdentityH;
 };
 
 }
diff --git a/Userland/Libraries/LibPDF/Document.cpp b/Userland/Libraries/LibPDF/Document.cpp
index 6097122ffcc..02112b2ed05 100644
--- a/Userland/Libraries/LibPDF/Document.cpp
+++ b/Userland/Libraries/LibPDF/Document.cpp
@@ -199,7 +199,7 @@ PDFErrorOr<void> Document::add_page_tree_node_to_page_tree(NonnullRefPtr<DictObj
     return {};
 }
 
-PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree(NonnullRefPtr<DictObject> tree, FlyString name)
+PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree(NonnullRefPtr<DictObject> tree, DeprecatedFlyString name)
 {
     if (tree->contains(CommonNames::Kids)) {
         return find_in_name_tree_nodes(tree->get_array(CommonNames::Kids), name);
@@ -210,7 +210,7 @@ PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree(NonnullRefPtr<Dict
     return find_in_key_value_array(key_value_names_array, name);
 }
 
-PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree_nodes(NonnullRefPtr<ArrayObject> siblings, FlyString name)
+PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree_nodes(NonnullRefPtr<ArrayObject> siblings, DeprecatedFlyString name)
 {
     for (size_t i = 0; i < siblings->size(); i++) {
         auto sibling = TRY(resolve_to<DictObject>(siblings->at(i)));
@@ -226,7 +226,7 @@ PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_name_tree_nodes(NonnullRefPt
     return Error { Error::Type::MalformedPDF, DeprecatedString::formatted("Didn't find node in name tree containing name {}", name) };
 }
 
-PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_key_value_array(NonnullRefPtr<ArrayObject> key_value_array, FlyString name)
+PDFErrorOr<NonnullRefPtr<Object>> Document::find_in_key_value_array(NonnullRefPtr<ArrayObject> key_value_array, DeprecatedFlyString name)
 {
     if (key_value_array->size() % 2 == 1)
         return Error { Error::Type::MalformedPDF, "key/value array has dangling key" };
@@ -306,7 +306,7 @@ PDFErrorOr<Destination> Document::create_destination_from_parameters(NonnullRefP
     return Destination { type, page_number_by_index_ref.get(page_ref.as_ref_index()), parameters };
 }
 
-PDFErrorOr<NonnullRefPtr<Object>> Document::get_inheritable_object(FlyString const& name, NonnullRefPtr<DictObject> object)
+PDFErrorOr<NonnullRefPtr<Object>> Document::get_inheritable_object(DeprecatedFlyString const& name, NonnullRefPtr<DictObject> object)
 {
     if (!object->contains(name)) {
         auto parent = TRY(object->get_dict(this, CommonNames::Parent));
@@ -352,7 +352,7 @@ PDFErrorOr<NonnullRefPtr<OutlineItem>> Document::build_outline_item(NonnullRefPt
             auto dest_arr = dest_obj->cast<ArrayObject>();
             outline_item->dest = TRY(create_destination_from_parameters(dest_arr, page_number_by_index_ref));
         } else if (dest_obj->is<NameObject>() || dest_obj->is<StringObject>()) {
-            FlyString dest_name;
+            DeprecatedFlyString dest_name;
             if (dest_obj->is<NameObject>())
                 dest_name = dest_obj->cast<NameObject>()->name();
             else
diff --git a/Userland/Libraries/LibPDF/Document.h b/Userland/Libraries/LibPDF/Document.h
index 2074af94558..85a64baa00b 100644
--- a/Userland/Libraries/LibPDF/Document.h
+++ b/Userland/Libraries/LibPDF/Document.h
@@ -138,11 +138,11 @@ private:
     PDFErrorOr<Destination> create_destination_from_parameters(NonnullRefPtr<ArrayObject>, HashMap<u32, u32> const&);
     PDFErrorOr<Destination> create_destination_from_dictionary_entry(NonnullRefPtr<Object> const& entry, HashMap<u32, u32> const& page_number_by_index_ref);
 
-    PDFErrorOr<NonnullRefPtr<Object>> get_inheritable_object(FlyString const& name, NonnullRefPtr<DictObject>);
+    PDFErrorOr<NonnullRefPtr<Object>> get_inheritable_object(DeprecatedFlyString const& name, NonnullRefPtr<DictObject>);
 
-    PDFErrorOr<NonnullRefPtr<Object>> find_in_name_tree(NonnullRefPtr<DictObject> root, FlyString name);
-    PDFErrorOr<NonnullRefPtr<Object>> find_in_name_tree_nodes(NonnullRefPtr<ArrayObject> siblings, FlyString name);
-    PDFErrorOr<NonnullRefPtr<Object>> find_in_key_value_array(NonnullRefPtr<ArrayObject> key_value_array, FlyString name);
+    PDFErrorOr<NonnullRefPtr<Object>> find_in_name_tree(NonnullRefPtr<DictObject> root, DeprecatedFlyString name);
+    PDFErrorOr<NonnullRefPtr<Object>> find_in_name_tree_nodes(NonnullRefPtr<ArrayObject> siblings, DeprecatedFlyString name);
+    PDFErrorOr<NonnullRefPtr<Object>> find_in_key_value_array(NonnullRefPtr<ArrayObject> key_value_array, DeprecatedFlyString name);
 
     NonnullRefPtr<DocumentParser> m_parser;
     RefPtr<DictObject> m_catalog;
diff --git a/Userland/Libraries/LibPDF/Filter.cpp b/Userland/Libraries/LibPDF/Filter.cpp
index 626cb1caa83..8898e010eb2 100644
--- a/Userland/Libraries/LibPDF/Filter.cpp
+++ b/Userland/Libraries/LibPDF/Filter.cpp
@@ -12,7 +12,7 @@
 
 namespace PDF {
 
-ErrorOr<ByteBuffer> Filter::decode(ReadonlyBytes bytes, FlyString const& encoding_type, RefPtr<DictObject> decode_parms)
+ErrorOr<ByteBuffer> Filter::decode(ReadonlyBytes bytes, DeprecatedFlyString const& encoding_type, RefPtr<DictObject> decode_parms)
 {
     int predictor = 1;
     int columns = 1;
diff --git a/Userland/Libraries/LibPDF/Filter.h b/Userland/Libraries/LibPDF/Filter.h
index dd68eb36e64..e3d37705f0d 100644
--- a/Userland/Libraries/LibPDF/Filter.h
+++ b/Userland/Libraries/LibPDF/Filter.h
@@ -7,15 +7,15 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Error.h>
-#include <AK/FlyString.h>
 #include <LibPDF/ObjectDerivatives.h>
 
 namespace PDF {
 
 class Filter {
 public:
-    static ErrorOr<ByteBuffer> decode(ReadonlyBytes bytes, FlyString const& encoding_type, RefPtr<DictObject> decode_parms);
+    static ErrorOr<ByteBuffer> decode(ReadonlyBytes bytes, DeprecatedFlyString const& encoding_type, RefPtr<DictObject> decode_parms);
 
 private:
     static ErrorOr<ByteBuffer> decode_ascii_hex(ReadonlyBytes bytes);
diff --git a/Userland/Libraries/LibPDF/Fonts/PDFFont.cpp b/Userland/Libraries/LibPDF/Fonts/PDFFont.cpp
index ab05e95904d..3be8446a7b1 100644
--- a/Userland/Libraries/LibPDF/Fonts/PDFFont.cpp
+++ b/Userland/Libraries/LibPDF/Fonts/PDFFont.cpp
@@ -14,7 +14,7 @@
 
 namespace PDF {
 
-static bool is_standard_latin_font(FlyString const& font)
+static bool is_standard_latin_font(DeprecatedFlyString const& font)
 {
     return font.is_one_of(
         "Times-Roman", "TimesNewRoman",
diff --git a/Userland/Libraries/LibPDF/Object.h b/Userland/Libraries/LibPDF/Object.h
index 0b3237e4a79..e64458fa8fc 100644
--- a/Userland/Libraries/LibPDF/Object.h
+++ b/Userland/Libraries/LibPDF/Object.h
@@ -7,7 +7,7 @@
 #pragma once
 
 #include <AK/Debug.h>
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Format.h>
 #include <AK/RefCounted.h>
 #include <AK/SourceLocation.h>
diff --git a/Userland/Libraries/LibPDF/ObjectDerivatives.cpp b/Userland/Libraries/LibPDF/ObjectDerivatives.cpp
index c86f59c2e48..7d59deaf57f 100644
--- a/Userland/Libraries/LibPDF/ObjectDerivatives.cpp
+++ b/Userland/Libraries/LibPDF/ObjectDerivatives.cpp
@@ -15,33 +15,33 @@ PDFErrorOr<NonnullRefPtr<Object>> ArrayObject::get_object_at(Document* document,
     return document->resolve_to<Object>(at(index));
 }
 
-PDFErrorOr<NonnullRefPtr<Object>> DictObject::get_object(Document* document, FlyString const& key) const
+PDFErrorOr<NonnullRefPtr<Object>> DictObject::get_object(Document* document, DeprecatedFlyString const& key) const
 {
     return document->resolve_to<Object>(get_value(key));
 }
 
-#define DEFINE_ACCESSORS(class_name, snake_name)                                                                       \
-    PDFErrorOr<NonnullRefPtr<class_name>> ArrayObject::get_##snake_name##_at(Document* document, size_t index) const   \
-    {                                                                                                                  \
-        if (index >= m_elements.size())                                                                                \
-            return Error { Error::Type::Internal, "Out of bounds array access" };                                      \
-        return document->resolve_to<class_name>(m_elements[index]);                                                    \
-    }                                                                                                                  \
-                                                                                                                       \
-    NonnullRefPtr<class_name> ArrayObject::get_##snake_name##_at(size_t index) const                                   \
-    {                                                                                                                  \
-        VERIFY(index < m_elements.size());                                                                             \
-        return cast_to<class_name>(m_elements[index]);                                                                 \
-    }                                                                                                                  \
-                                                                                                                       \
-    PDFErrorOr<NonnullRefPtr<class_name>> DictObject::get_##snake_name(Document* document, FlyString const& key) const \
-    {                                                                                                                  \
-        return document->resolve_to<class_name>(get_value(key));                                                       \
-    }                                                                                                                  \
-                                                                                                                       \
-    NonnullRefPtr<class_name> DictObject::get_##snake_name(FlyString const& key) const                                 \
-    {                                                                                                                  \
-        return cast_to<class_name>(get_value(key));                                                                    \
+#define DEFINE_ACCESSORS(class_name, snake_name)                                                                                 \
+    PDFErrorOr<NonnullRefPtr<class_name>> ArrayObject::get_##snake_name##_at(Document* document, size_t index) const             \
+    {                                                                                                                            \
+        if (index >= m_elements.size())                                                                                          \
+            return Error { Error::Type::Internal, "Out of bounds array access" };                                                \
+        return document->resolve_to<class_name>(m_elements[index]);                                                              \
+    }                                                                                                                            \
+                                                                                                                                 \
+    NonnullRefPtr<class_name> ArrayObject::get_##snake_name##_at(size_t index) const                                             \
+    {                                                                                                                            \
+        VERIFY(index < m_elements.size());                                                                                       \
+        return cast_to<class_name>(m_elements[index]);                                                                           \
+    }                                                                                                                            \
+                                                                                                                                 \
+    PDFErrorOr<NonnullRefPtr<class_name>> DictObject::get_##snake_name(Document* document, DeprecatedFlyString const& key) const \
+    {                                                                                                                            \
+        return document->resolve_to<class_name>(get_value(key));                                                                 \
+    }                                                                                                                            \
+                                                                                                                                 \
+    NonnullRefPtr<class_name> DictObject::get_##snake_name(DeprecatedFlyString const& key) const                                 \
+    {                                                                                                                            \
+        return cast_to<class_name>(get_value(key));                                                                              \
     }
 
 ENUMERATE_OBJECT_TYPES(DEFINE_ACCESSORS)
diff --git a/Userland/Libraries/LibPDF/ObjectDerivatives.h b/Userland/Libraries/LibPDF/ObjectDerivatives.h
index 1078c7c9170..2cc5263f419 100644
--- a/Userland/Libraries/LibPDF/ObjectDerivatives.h
+++ b/Userland/Libraries/LibPDF/ObjectDerivatives.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/HashMap.h>
 #include <AK/RefCounted.h>
 #include <AK/SourceLocation.h>
@@ -44,14 +44,14 @@ private:
 
 class NameObject final : public Object {
 public:
-    explicit NameObject(FlyString name)
+    explicit NameObject(DeprecatedFlyString name)
         : m_name(move(name))
     {
     }
 
     ~NameObject() override = default;
 
-    [[nodiscard]] ALWAYS_INLINE FlyString const& name() const { return m_name; }
+    [[nodiscard]] ALWAYS_INLINE DeprecatedFlyString const& name() const { return m_name; }
 
     char const* type_name() const override { return "name"; }
     DeprecatedString to_deprecated_string(int indent) const override;
@@ -60,7 +60,7 @@ protected:
     bool is_name() const override { return true; }
 
 private:
-    FlyString m_name;
+    DeprecatedFlyString m_name;
 };
 
 class ArrayObject final : public Object {
@@ -106,14 +106,14 @@ private:
 
 class DictObject final : public Object {
 public:
-    explicit DictObject(HashMap<FlyString, Value> map)
+    explicit DictObject(HashMap<DeprecatedFlyString, Value> map)
         : m_map(move(map))
     {
     }
 
     ~DictObject() override = default;
 
-    [[nodiscard]] ALWAYS_INLINE HashMap<FlyString, Value> const& map() const { return m_map; }
+    [[nodiscard]] ALWAYS_INLINE HashMap<DeprecatedFlyString, Value> const& map() const { return m_map; }
 
     template<typename... Args>
     bool contains(Args&&... keys) const { return (m_map.contains(keys) && ...); }
@@ -121,20 +121,20 @@ public:
     template<typename... Args>
     bool contains_any_of(Args&&... keys) const { return (m_map.contains(keys) || ...); }
 
-    ALWAYS_INLINE Optional<Value> get(FlyString const& key) const { return m_map.get(key); }
+    ALWAYS_INLINE Optional<Value> get(DeprecatedFlyString const& key) const { return m_map.get(key); }
 
-    Value get_value(FlyString const& key) const
+    Value get_value(DeprecatedFlyString const& key) const
     {
         auto value = get(key);
         VERIFY(value.has_value());
         return value.value();
     }
 
-    PDFErrorOr<NonnullRefPtr<Object>> get_object(Document*, FlyString const& key) const;
+    PDFErrorOr<NonnullRefPtr<Object>> get_object(Document*, DeprecatedFlyString const& key) const;
 
-#define DEFINE_GETTER(class_name, snake_name)                                                      \
-    PDFErrorOr<NonnullRefPtr<class_name>> get_##snake_name(Document*, FlyString const& key) const; \
-    NonnullRefPtr<class_name> get_##snake_name(FlyString const& key) const;
+#define DEFINE_GETTER(class_name, snake_name)                                                                \
+    PDFErrorOr<NonnullRefPtr<class_name>> get_##snake_name(Document*, DeprecatedFlyString const& key) const; \
+    NonnullRefPtr<class_name> get_##snake_name(DeprecatedFlyString const& key) const;
     ENUMERATE_OBJECT_TYPES(DEFINE_GETTER)
 #undef DEFINE_GETTER
 
@@ -148,7 +148,7 @@ protected:
     bool is_dict() const override { return true; }
 
 private:
-    HashMap<FlyString, Value> m_map;
+    HashMap<DeprecatedFlyString, Value> m_map;
 };
 
 class StreamObject : public Object {
diff --git a/Userland/Libraries/LibPDF/Parser.cpp b/Userland/Libraries/LibPDF/Parser.cpp
index ba33e3d17e3..a51f0f8e53a 100644
--- a/Userland/Libraries/LibPDF/Parser.cpp
+++ b/Userland/Libraries/LibPDF/Parser.cpp
@@ -418,7 +418,7 @@ PDFErrorOr<NonnullRefPtr<DictObject>> Parser::parse_dict()
         return error("Expected dict to start with \"<<\"");
 
     m_reader.consume_whitespace();
-    HashMap<FlyString, Value> map;
+    HashMap<DeprecatedFlyString, Value> map;
 
     while (!m_reader.done()) {
         if (m_reader.matches(">>"))
@@ -479,7 +479,7 @@ PDFErrorOr<NonnullRefPtr<StreamObject>> Parser::parse_stream(NonnullRefPtr<DictO
         m_document->security_handler()->decrypt(stream_object, m_current_reference_stack.last());
 
     if (dict->contains(CommonNames::Filter)) {
-        Vector<FlyString> filters;
+        Vector<DeprecatedFlyString> filters;
 
         // We may either get a single filter or an array of cascading filters
         auto filter_object = TRY(dict->get_object(m_document, CommonNames::Filter));
diff --git a/Userland/Libraries/LibPDF/Renderer.cpp b/Userland/Libraries/LibPDF/Renderer.cpp
index c41f1ba1243..20716237ffe 100644
--- a/Userland/Libraries/LibPDF/Renderer.cpp
+++ b/Userland/Libraries/LibPDF/Renderer.cpp
@@ -773,7 +773,7 @@ PDFErrorOr<NonnullRefPtr<Gfx::Bitmap>> Renderer::load_image(NonnullRefPtr<Stream
     auto width = image_dict->get_value(CommonNames::Width).get<int>();
     auto height = image_dict->get_value(CommonNames::Height).get<int>();
 
-    auto is_filter = [&](FlyString const& name) {
+    auto is_filter = [&](DeprecatedFlyString const& name) {
         if (filter_object->is<NameObject>())
             return filter_object->cast<NameObject>()->name() == name;
         auto filters = filter_object->cast<ArrayObject>();
diff --git a/Userland/Libraries/LibRegex/RegexMatch.h b/Userland/Libraries/LibRegex/RegexMatch.h
index df05526e8a0..670e06e80d2 100644
--- a/Userland/Libraries/LibRegex/RegexMatch.h
+++ b/Userland/Libraries/LibRegex/RegexMatch.h
@@ -9,8 +9,8 @@
 #include "Forward.h"
 #include "RegexOptions.h"
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashMap.h>
 #include <AK/MemMem.h>
 #include <AK/RedBlackTree.h>
@@ -558,7 +558,7 @@ private:
 
 class Match final {
 private:
-    Optional<FlyString> string;
+    Optional<DeprecatedFlyString> string;
 
 public:
     Match() = default;
@@ -603,7 +603,7 @@ public:
     }
 
     RegexStringView view {};
-    Optional<FlyString> capture_group_name {};
+    Optional<DeprecatedFlyString> capture_group_name {};
     size_t line { 0 };
     size_t column { 0 };
     size_t global_offset { 0 };
diff --git a/Userland/Libraries/LibRegex/RegexParser.cpp b/Userland/Libraries/LibRegex/RegexParser.cpp
index e939b4779bf..bc6c2fc7d08 100644
--- a/Userland/Libraries/LibRegex/RegexParser.cpp
+++ b/Userland/Libraries/LibRegex/RegexParser.cpp
@@ -2427,7 +2427,7 @@ bool ECMA262Parser::parse_unicode_property_escape(PropertyEscape& property, bool
         [](Empty&) -> bool { VERIFY_NOT_REACHED(); });
 }
 
-FlyString ECMA262Parser::read_capture_group_specifier(bool take_starting_angle_bracket)
+DeprecatedFlyString ECMA262Parser::read_capture_group_specifier(bool take_starting_angle_bracket)
 {
     static auto id_start_category = Unicode::property_from_string("ID_Start"sv);
     static auto id_continue_category = Unicode::property_from_string("ID_Continue"sv);
@@ -2530,7 +2530,7 @@ FlyString ECMA262Parser::read_capture_group_specifier(bool take_starting_angle_b
         builder.append_code_point(code_point);
     }
 
-    FlyString name = builder.build();
+    DeprecatedFlyString name = builder.build();
     if (!hit_end || name.is_empty())
         set_error(Error::InvalidNameForCaptureGroup);
 
diff --git a/Userland/Libraries/LibRegex/RegexParser.h b/Userland/Libraries/LibRegex/RegexParser.h
index cfc0db56bf0..8ae30289f4a 100644
--- a/Userland/Libraries/LibRegex/RegexParser.h
+++ b/Userland/Libraries/LibRegex/RegexParser.h
@@ -53,7 +53,7 @@ public:
         size_t match_length_minimum;
         Error error;
         Token error_token;
-        Vector<FlyString> capture_groups;
+        Vector<DeprecatedFlyString> capture_groups;
         AllOptions options;
     };
 
@@ -111,7 +111,7 @@ protected:
         size_t repetition_mark_count { 0 };
         AllOptions regex_options;
         HashMap<int, size_t> capture_group_minimum_lengths;
-        HashMap<FlyString, NamedCaptureGroup> named_capture_groups;
+        HashMap<DeprecatedFlyString, NamedCaptureGroup> named_capture_groups;
 
         explicit ParserState(Lexer& lexer)
             : lexer(lexer)
@@ -234,7 +234,7 @@ private:
     };
     StringView read_digits_as_string(ReadDigitsInitialZeroState initial_zero = ReadDigitsInitialZeroState::Allow, bool hex = false, int max_count = -1, int min_count = -1);
     Optional<unsigned> read_digits(ReadDigitsInitialZeroState initial_zero = ReadDigitsInitialZeroState::Allow, bool hex = false, int max_count = -1, int min_count = -1);
-    FlyString read_capture_group_specifier(bool take_starting_angle_bracket = false);
+    DeprecatedFlyString read_capture_group_specifier(bool take_starting_angle_bracket = false);
 
     struct Script {
         Unicode::Script script {};
diff --git a/Userland/Libraries/LibVideo/Containers/Matroska/Document.h b/Userland/Libraries/LibVideo/Containers/Matroska/Document.h
index d827be8d02b..325cb32e120 100644
--- a/Userland/Libraries/LibVideo/Containers/Matroska/Document.h
+++ b/Userland/Libraries/LibVideo/Containers/Matroska/Document.h
@@ -7,8 +7,8 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashMap.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <AK/OwnPtr.h>
@@ -116,10 +116,10 @@ public:
     void set_track_uid(u64 track_uid) { m_track_uid = track_uid; }
     TrackType track_type() const { return m_track_type; }
     void set_track_type(TrackType track_type) { m_track_type = track_type; }
-    FlyString language() const { return m_language; }
-    void set_language(FlyString const& language) { m_language = language; }
-    FlyString codec_id() const { return m_codec_id; }
-    void set_codec_id(FlyString const& codec_id) { m_codec_id = codec_id; }
+    DeprecatedFlyString language() const { return m_language; }
+    void set_language(DeprecatedFlyString const& language) { m_language = language; }
+    DeprecatedFlyString codec_id() const { return m_codec_id; }
+    void set_codec_id(DeprecatedFlyString const& codec_id) { m_codec_id = codec_id; }
     double timestamp_scale() const { return m_timestamp_scale; }
     void set_timestamp_scale(double timestamp_scale) { m_timestamp_scale = timestamp_scale; }
     u64 codec_delay() const { return m_codec_delay; }
@@ -145,8 +145,8 @@ private:
     u64 m_track_number { 0 };
     u64 m_track_uid { 0 };
     TrackType m_track_type { Invalid };
-    FlyString m_language = "eng";
-    FlyString m_codec_id;
+    DeprecatedFlyString m_language = "eng";
+    DeprecatedFlyString m_codec_id;
     double m_timestamp_scale { 1 };
     u64 m_codec_delay { 0 };
     u64 m_timestamp_offset { 0 };
diff --git a/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.cpp b/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.cpp
index 29856802453..0c6776141e3 100644
--- a/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.cpp
+++ b/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.cpp
@@ -302,7 +302,7 @@ JS::Value LegacyPlatformObject::item_value(size_t) const
     return JS::js_undefined();
 }
 
-JS::Value LegacyPlatformObject::named_item_value(FlyString const&) const
+JS::Value LegacyPlatformObject::named_item_value(DeprecatedFlyString const&) const
 {
     return JS::js_undefined();
 }
diff --git a/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.h b/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.h
index b04192c970b..bf8955fb3ca 100644
--- a/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.h
+++ b/Userland/Libraries/LibWeb/Bindings/LegacyPlatformObject.h
@@ -29,7 +29,7 @@ public:
     JS::ThrowCompletionOr<Optional<JS::PropertyDescriptor>> legacy_platform_object_get_own_property_for_set_slot(JS::PropertyKey const&) const;
 
     virtual JS::Value item_value(size_t index) const;
-    virtual JS::Value named_item_value(FlyString const& name) const;
+    virtual JS::Value named_item_value(DeprecatedFlyString const& name) const;
     virtual Vector<DeprecatedString> supported_property_names() const;
     virtual bool is_supported_property_index(u32) const;
 
diff --git a/Userland/Libraries/LibWeb/Bindings/LocationObject.cpp b/Userland/Libraries/LibWeb/Bindings/LocationObject.cpp
index b8d994e77d9..ae44fe8c33e 100644
--- a/Userland/Libraries/LibWeb/Bindings/LocationObject.cpp
+++ b/Userland/Libraries/LibWeb/Bindings/LocationObject.cpp
@@ -5,7 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/StringBuilder.h>
 #include <LibJS/Heap/MarkedVector.h>
 #include <LibJS/Runtime/Completion.h>
diff --git a/Userland/Libraries/LibWeb/CSS/FontFace.cpp b/Userland/Libraries/LibWeb/CSS/FontFace.cpp
index 4618ccb6955..b4b585258c9 100644
--- a/Userland/Libraries/LibWeb/CSS/FontFace.cpp
+++ b/Userland/Libraries/LibWeb/CSS/FontFace.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::CSS {
 
-FontFace::FontFace(FlyString font_family, Vector<Source> sources, Vector<UnicodeRange> unicode_ranges)
+FontFace::FontFace(DeprecatedFlyString font_family, Vector<Source> sources, Vector<UnicodeRange> unicode_ranges)
     : m_font_family(move(font_family))
     , m_sources(move(sources))
     , m_unicode_ranges(move(unicode_ranges))
diff --git a/Userland/Libraries/LibWeb/CSS/FontFace.h b/Userland/Libraries/LibWeb/CSS/FontFace.h
index cbabd7a018f..77cd7f9e8fa 100644
--- a/Userland/Libraries/LibWeb/CSS/FontFace.h
+++ b/Userland/Libraries/LibWeb/CSS/FontFace.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/URL.h>
 #include <LibWeb/CSS/UnicodeRange.h>
 
@@ -17,19 +17,19 @@ public:
     struct Source {
         AK::URL url;
         // FIXME: Do we need to keep this around, or is it only needed to discard unwanted formats during parsing?
-        Optional<FlyString> format;
+        Optional<DeprecatedFlyString> format;
     };
 
-    FontFace(FlyString font_family, Vector<Source> sources, Vector<UnicodeRange> unicode_ranges);
+    FontFace(DeprecatedFlyString font_family, Vector<Source> sources, Vector<UnicodeRange> unicode_ranges);
     ~FontFace() = default;
 
-    FlyString font_family() const { return m_font_family; }
+    DeprecatedFlyString font_family() const { return m_font_family; }
     Vector<Source> const& sources() const { return m_sources; }
     Vector<UnicodeRange> const& unicode_ranges() const { return m_unicode_ranges; }
     // FIXME: font-style, font-weight, font-stretch, font-feature-settings
 
 private:
-    FlyString m_font_family;
+    DeprecatedFlyString m_font_family;
     Vector<Source> m_sources;
     Vector<UnicodeRange> m_unicode_ranges;
 };
diff --git a/Userland/Libraries/LibWeb/CSS/MediaQuery.h b/Userland/Libraries/LibWeb/CSS/MediaQuery.h
index 9ea69ee2eb9..ed31e57aa56 100644
--- a/Userland/Libraries/LibWeb/CSS/MediaQuery.h
+++ b/Userland/Libraries/LibWeb/CSS/MediaQuery.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/NonnullOwnPtrVector.h>
 #include <AK/NonnullRefPtr.h>
 #include <AK/Optional.h>
diff --git a/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.cpp b/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.cpp
index 66977a579ca..f33518add55 100644
--- a/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.cpp
+++ b/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.cpp
@@ -10,12 +10,12 @@
 
 namespace Web::CSS {
 
-MediaQueryListEvent* MediaQueryListEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, MediaQueryListEventInit const& event_init)
+MediaQueryListEvent* MediaQueryListEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, MediaQueryListEventInit const& event_init)
 {
     return realm.heap().allocate<MediaQueryListEvent>(realm, realm, event_name, event_init);
 }
 
-MediaQueryListEvent::MediaQueryListEvent(JS::Realm& realm, FlyString const& event_name, MediaQueryListEventInit const& event_init)
+MediaQueryListEvent::MediaQueryListEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, MediaQueryListEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_media(event_init.media)
     , m_matches(event_init.matches)
diff --git a/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.h b/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.h
index 80fbdbe6c07..8ab1863441f 100644
--- a/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.h
+++ b/Userland/Libraries/LibWeb/CSS/MediaQueryListEvent.h
@@ -19,7 +19,7 @@ class MediaQueryListEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(MediaQueryListEvent, DOM::Event);
 
 public:
-    static MediaQueryListEvent* construct_impl(JS::Realm&, FlyString const& event_name, MediaQueryListEventInit const& event_init = {});
+    static MediaQueryListEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, MediaQueryListEventInit const& event_init = {});
 
     virtual ~MediaQueryListEvent() override;
 
@@ -27,7 +27,7 @@ public:
     bool matches() const { return m_matches; }
 
 private:
-    MediaQueryListEvent(JS::Realm&, FlyString const& event_name, MediaQueryListEventInit const& event_init);
+    MediaQueryListEvent(JS::Realm&, DeprecatedFlyString const& event_name, MediaQueryListEventInit const& event_init);
 
     DeprecatedString m_media;
     bool m_matches;
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Declaration.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Declaration.cpp
index 572efe143c8..e38aa497fac 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Declaration.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Declaration.cpp
@@ -10,7 +10,7 @@
 
 namespace Web::CSS::Parser {
 
-Declaration::Declaration(FlyString name, Vector<ComponentValue> values, Important important)
+Declaration::Declaration(DeprecatedFlyString name, Vector<ComponentValue> values, Important important)
     : m_name(move(name))
     , m_values(move(values))
     , m_important(move(important))
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Declaration.h b/Userland/Libraries/LibWeb/CSS/Parser/Declaration.h
index fd0e2e1c77c..35f0dc1a6c9 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Declaration.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Declaration.h
@@ -15,7 +15,7 @@ namespace Web::CSS::Parser {
 
 class Declaration {
 public:
-    Declaration(FlyString name, Vector<ComponentValue> values, Important);
+    Declaration(DeprecatedFlyString name, Vector<ComponentValue> values, Important);
     ~Declaration();
 
     StringView name() const { return m_name; }
@@ -25,7 +25,7 @@ public:
     DeprecatedString to_deprecated_string() const;
 
 private:
-    FlyString m_name;
+    DeprecatedFlyString m_name;
     Vector<ComponentValue> m_values;
     Important m_important { Important::No };
 };
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Function.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Function.cpp
index fdd15a7359a..8d4a06c1393 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Function.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Function.cpp
@@ -10,7 +10,7 @@
 
 namespace Web::CSS::Parser {
 
-Function::Function(FlyString name, Vector<ComponentValue>&& values)
+Function::Function(DeprecatedFlyString name, Vector<ComponentValue>&& values)
     : m_name(move(name))
     , m_values(move(values))
 {
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Function.h b/Userland/Libraries/LibWeb/CSS/Parser/Function.h
index f45be687610..6eb161bbc8a 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Function.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Function.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/RefCounted.h>
 #include <AK/Vector.h>
 #include <LibWeb/CSS/Parser/ComponentValue.h>
@@ -18,7 +18,7 @@ namespace Web::CSS::Parser {
 
 class Function : public RefCounted<Function> {
 public:
-    static NonnullRefPtr<Function> create(FlyString name, Vector<ComponentValue>&& values)
+    static NonnullRefPtr<Function> create(DeprecatedFlyString name, Vector<ComponentValue>&& values)
     {
         return adopt_ref(*new Function(move(name), move(values)));
     }
@@ -31,9 +31,9 @@ public:
     DeprecatedString to_deprecated_string() const;
 
 private:
-    Function(FlyString name, Vector<ComponentValue>&& values);
+    Function(DeprecatedFlyString name, Vector<ComponentValue>&& values);
 
-    FlyString m_name;
+    DeprecatedFlyString m_name;
     Vector<ComponentValue> m_values;
 };
 }
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
index c45a01eb413..d7397821da7 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -561,7 +561,7 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
                 return ParseError::SyntaxError;
             }
             // FIXME: Support multiple, comma-separated, language ranges.
-            Vector<FlyString> languages;
+            Vector<DeprecatedFlyString> languages;
             languages.append(pseudo_function.values().first().token().to_deprecated_string());
             return Selector::SimpleSelector {
                 .type = Selector::SimpleSelector::Type::PseudoClass,
@@ -1518,7 +1518,7 @@ NonnullRefPtr<Rule> Parser::consume_an_at_rule(TokenStream<T>& tokens)
 
     // Create a new at-rule with its name set to the value of the current input token, its prelude initially set to an empty list, and its value initially set to nothing.
     // NOTE: We create the Rule fully initialized when we return it instead.
-    FlyString at_rule_name = ((Token)name_ident).at_keyword();
+    DeprecatedFlyString at_rule_name = ((Token)name_ident).at_keyword();
     Vector<ComponentValue> prelude;
     RefPtr<Block> block;
 
@@ -1801,7 +1801,7 @@ NonnullRefPtr<Function> Parser::consume_a_function(TokenStream<T>& tokens)
     // Create a function with its name equal to the value of the current input token
     // and with its value initially set to an empty list.
     // NOTE: We create the Function fully initialized when we return it instead.
-    FlyString function_name = ((Token)name_ident).function();
+    DeprecatedFlyString function_name = ((Token)name_ident).function();
     Vector<ComponentValue> function_values;
 
     // Repeatedly consume the next input token and process it as follows:
@@ -1856,7 +1856,7 @@ Optional<Declaration> Parser::consume_a_declaration(TokenStream<T>& tokens)
     // Create a new declaration with its name set to the value of the current input token
     // and its value initially set to the empty list.
     // NOTE: We create a fully-initialized Declaration just before returning it instead.
-    FlyString declaration_name = ((Token)token).ident();
+    DeprecatedFlyString declaration_name = ((Token)token).ident();
     Vector<ComponentValue> declaration_values;
     Important declaration_important = Important::No;
 
@@ -5289,7 +5289,7 @@ CSSRule* Parser::parse_font_face_rule(TokenStream<ComponentValue>& tokens)
 {
     auto declarations_and_at_rules = parse_a_list_of_declarations(tokens);
 
-    Optional<FlyString> font_family;
+    Optional<DeprecatedFlyString> font_family;
     Vector<FontFace::Source> src;
     Vector<UnicodeRange> unicode_range;
 
@@ -5412,7 +5412,7 @@ Vector<FontFace::Source> Parser::parse_font_face_src(TokenStream<ComponentValue>
         // FIXME: Implement optional tech() function from CSS-Fonts-4.
         if (auto maybe_url = parse_url_function(first, AllowedDataUrlType::Font); maybe_url.has_value()) {
             auto url = maybe_url.release_value();
-            Optional<FlyString> format;
+            Optional<DeprecatedFlyString> format;
 
             source_tokens.skip_whitespace();
             if (!source_tokens.has_next_token()) {
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Rule.cpp b/Userland/Libraries/LibWeb/CSS/Parser/Rule.cpp
index 7b313764495..e9cbfc1d593 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Rule.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Rule.cpp
@@ -10,7 +10,7 @@
 
 namespace Web::CSS::Parser {
 
-Rule::Rule(Rule::Type type, FlyString name, Vector<ComponentValue> prelude, RefPtr<Block> block)
+Rule::Rule(Rule::Type type, DeprecatedFlyString name, Vector<ComponentValue> prelude, RefPtr<Block> block)
     : m_type(type)
     , m_at_rule_name(move(name))
     , m_prelude(move(prelude))
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Rule.h b/Userland/Libraries/LibWeb/CSS/Parser/Rule.h
index 7afd9135389..dfc9a7f8954 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Rule.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Rule.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/RefCounted.h>
 #include <AK/Vector.h>
 #include <LibWeb/CSS/Parser/Block.h>
@@ -22,7 +22,7 @@ public:
         Qualified,
     };
 
-    static NonnullRefPtr<Rule> make_at_rule(FlyString name, Vector<ComponentValue> prelude, RefPtr<Block> block)
+    static NonnullRefPtr<Rule> make_at_rule(DeprecatedFlyString name, Vector<ComponentValue> prelude, RefPtr<Block> block)
     {
         return adopt_ref(*new Rule(Type::At, move(name), move(prelude), move(block)));
     }
@@ -44,10 +44,10 @@ public:
     DeprecatedString to_deprecated_string() const;
 
 private:
-    Rule(Type, FlyString name, Vector<ComponentValue> prelude, RefPtr<Block>);
+    Rule(Type, DeprecatedFlyString name, Vector<ComponentValue> prelude, RefPtr<Block>);
 
     Type const m_type;
-    FlyString m_at_rule_name;
+    DeprecatedFlyString m_at_rule_name;
     Vector<ComponentValue> m_prelude;
     RefPtr<Block> m_block;
 };
diff --git a/Userland/Libraries/LibWeb/CSS/Parser/Token.h b/Userland/Libraries/LibWeb/CSS/Parser/Token.h
index 93fa0712f31..f1aed4d13bf 100644
--- a/Userland/Libraries/LibWeb/CSS/Parser/Token.h
+++ b/Userland/Libraries/LibWeb/CSS/Parser/Token.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Utf8View.h>
 #include <LibWeb/CSS/Number.h>
 
@@ -151,7 +151,7 @@ public:
     Position const& start_position() const { return m_start_position; }
     Position const& end_position() const { return m_end_position; }
 
-    static Token of_string(FlyString str)
+    static Token of_string(DeprecatedFlyString str)
     {
         Token token;
         token.m_type = Type::String;
@@ -178,7 +178,7 @@ public:
 private:
     Type m_type { Type::Invalid };
 
-    FlyString m_value;
+    DeprecatedFlyString m_value;
     Number m_number_value;
     HashType m_hash_type { HashType::Unrestricted };
 
diff --git a/Userland/Libraries/LibWeb/CSS/Selector.h b/Userland/Libraries/LibWeb/CSS/Selector.h
index 2dcb26db22b..ac180e5061f 100644
--- a/Userland/Libraries/LibWeb/CSS/Selector.h
+++ b/Userland/Libraries/LibWeb/CSS/Selector.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/NonnullRefPtrVector.h>
 #include <AK/RefCounted.h>
 #include <AK/Vector.h>
@@ -121,7 +121,7 @@ public:
             SelectorList argument_selector_list {};
 
             // Used for :lang(en-gb,dk)
-            Vector<FlyString> languages {};
+            Vector<DeprecatedFlyString> languages {};
         };
 
         struct Attribute {
@@ -140,20 +140,20 @@ public:
                 CaseInsensitiveMatch,
             };
             MatchType match_type;
-            FlyString name {};
+            DeprecatedFlyString name {};
             DeprecatedString value {};
             CaseType case_type;
         };
 
         struct Name {
-            Name(FlyString n)
+            Name(DeprecatedFlyString n)
                 : name(move(n))
                 , lowercase_name(name.to_lowercase())
             {
             }
 
-            FlyString name;
-            FlyString lowercase_name;
+            DeprecatedFlyString name;
+            DeprecatedFlyString lowercase_name;
         };
 
         Type type;
@@ -166,10 +166,10 @@ public:
         PseudoElement const& pseudo_element() const { return value.get<PseudoElement>(); }
         PseudoElement& pseudo_element() { return value.get<PseudoElement>(); }
 
-        FlyString const& name() const { return value.get<Name>().name; }
-        FlyString& name() { return value.get<Name>().name; }
-        FlyString const& lowercase_name() const { return value.get<Name>().lowercase_name; }
-        FlyString& lowercase_name() { return value.get<Name>().lowercase_name; }
+        DeprecatedFlyString const& name() const { return value.get<Name>().name; }
+        DeprecatedFlyString& name() { return value.get<Name>().name; }
+        DeprecatedFlyString const& lowercase_name() const { return value.get<Name>().lowercase_name; }
+        DeprecatedFlyString& lowercase_name() { return value.get<Name>().lowercase_name; }
 
         DeprecatedString serialize() const;
     };
diff --git a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
index b782a2c384a..116bdfa00db 100644
--- a/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
+++ b/Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
@@ -25,9 +25,9 @@
 namespace Web::SelectorEngine {
 
 // https://drafts.csswg.org/selectors-4/#the-lang-pseudo
-static inline bool matches_lang_pseudo_class(DOM::Element const& element, Vector<FlyString> const& languages)
+static inline bool matches_lang_pseudo_class(DOM::Element const& element, Vector<DeprecatedFlyString> const& languages)
 {
-    FlyString element_language;
+    DeprecatedFlyString element_language;
     for (auto const* e = &element; e; e = e->parent_element()) {
         auto lang = e->attribute(HTML::AttributeNames::lang);
         if (!lang.is_null()) {
diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
index da258345fd2..64c670b932a 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
@@ -43,7 +43,7 @@ StyleComputer::~StyleComputer() = default;
 
 class StyleComputer::FontLoader : public ResourceClient {
 public:
-    explicit FontLoader(StyleComputer& style_computer, FlyString family_name, AK::URL url)
+    explicit FontLoader(StyleComputer& style_computer, DeprecatedFlyString family_name, AK::URL url)
         : m_style_computer(style_computer)
         , m_family_name(move(family_name))
     {
@@ -105,7 +105,7 @@ private:
     }
 
     StyleComputer& m_style_computer;
-    FlyString m_family_name;
+    DeprecatedFlyString m_family_name;
     RefPtr<Gfx::VectorFont> m_vector_font;
 
     HashMap<float, NonnullRefPtr<Gfx::ScaledFont>> mutable m_cached_fonts;
@@ -571,7 +571,7 @@ static void set_property_expanding_shorthands(StyleProperties& style, CSS::Prope
     style.set_property(property_id, value);
 }
 
-static RefPtr<StyleValue> get_custom_property(DOM::Element const& element, FlyString const& custom_property_name)
+static RefPtr<StyleValue> get_custom_property(DOM::Element const& element, DeprecatedFlyString const& custom_property_name)
 {
     for (auto const* current_element = &element; current_element; current_element = current_element->parent_element()) {
         if (auto it = current_element->custom_properties().find(custom_property_name); it != current_element->custom_properties().end())
@@ -580,7 +580,7 @@ static RefPtr<StyleValue> get_custom_property(DOM::Element const& element, FlySt
     return nullptr;
 }
 
-bool StyleComputer::expand_variables(DOM::Element& element, StringView property_name, HashMap<FlyString, NonnullRefPtr<PropertyDependencyNode>>& dependencies, Parser::TokenStream<Parser::ComponentValue>& source, Vector<Parser::ComponentValue>& dest) const
+bool StyleComputer::expand_variables(DOM::Element& element, StringView property_name, HashMap<DeprecatedFlyString, NonnullRefPtr<PropertyDependencyNode>>& dependencies, Parser::TokenStream<Parser::ComponentValue>& source, Vector<Parser::ComponentValue>& dest) const
 {
     // Arbitrary large value chosen to avoid the billion-laughs attack.
     // https://www.w3.org/TR/css-variables-1/#long-variables
@@ -761,7 +761,7 @@ RefPtr<StyleValue> StyleComputer::resolve_unresolved_style_value(DOM::Element& e
     Parser::TokenStream unresolved_values_without_variables_expanded { unresolved.values() };
     Vector<Parser::ComponentValue> values_with_variables_expanded;
 
-    HashMap<FlyString, NonnullRefPtr<PropertyDependencyNode>> dependencies;
+    HashMap<DeprecatedFlyString, NonnullRefPtr<PropertyDependencyNode>> dependencies;
     if (!expand_variables(element, string_from_property_id(property_id), dependencies, unresolved_values_without_variables_expanded, values_with_variables_expanded))
         return {};
 
@@ -817,7 +817,7 @@ static ErrorOr<void> cascade_custom_properties(DOM::Element& element, Vector<Mat
     if (auto const* inline_style = verify_cast<PropertyOwningCSSStyleDeclaration>(element.inline_style()))
         needed_capacity += inline_style->custom_properties().size();
 
-    HashMap<FlyString, StyleProperty> custom_properties;
+    HashMap<DeprecatedFlyString, StyleProperty> custom_properties;
     TRY(custom_properties.try_ensure_capacity(needed_capacity));
 
     for (auto const& matching_rule : matching_rules) {
@@ -1444,7 +1444,7 @@ CSSPixelRect StyleComputer::viewport_rect() const
     return {};
 }
 
-void StyleComputer::did_load_font([[maybe_unused]] FlyString const& family_name)
+void StyleComputer::did_load_font([[maybe_unused]] DeprecatedFlyString const& family_name)
 {
     document().invalidate_layout();
 }
diff --git a/Userland/Libraries/LibWeb/CSS/StyleComputer.h b/Userland/Libraries/LibWeb/CSS/StyleComputer.h
index 4482ac6027c..5d9c79dd9f9 100644
--- a/Userland/Libraries/LibWeb/CSS/StyleComputer.h
+++ b/Userland/Libraries/LibWeb/CSS/StyleComputer.h
@@ -73,7 +73,7 @@ public:
 
     Gfx::Font const& initial_font() const;
 
-    void did_load_font(FlyString const& family_name);
+    void did_load_font(DeprecatedFlyString const& family_name);
 
     void load_fonts_from_sheet(CSSStyleSheet const&);
 
@@ -87,7 +87,7 @@ private:
     void compute_defaulted_property_value(StyleProperties&, DOM::Element const*, CSS::PropertyID, Optional<CSS::Selector::PseudoElement>) const;
 
     RefPtr<StyleValue> resolve_unresolved_style_value(DOM::Element&, PropertyID, UnresolvedStyleValue const&) const;
-    bool expand_variables(DOM::Element&, StringView property_name, HashMap<FlyString, NonnullRefPtr<PropertyDependencyNode>>& dependencies, Parser::TokenStream<Parser::ComponentValue>& source, Vector<Parser::ComponentValue>& dest) const;
+    bool expand_variables(DOM::Element&, StringView property_name, HashMap<DeprecatedFlyString, NonnullRefPtr<PropertyDependencyNode>>& dependencies, Parser::TokenStream<Parser::ComponentValue>& source, Vector<Parser::ComponentValue>& dest) const;
     bool expand_unresolved_values(DOM::Element&, StringView property_name, Parser::TokenStream<Parser::ComponentValue>& source, Vector<Parser::ComponentValue>& dest) const;
 
     template<typename Callback>
@@ -109,9 +109,9 @@ private:
     DOM::Document& m_document;
 
     struct RuleCache {
-        HashMap<FlyString, Vector<MatchingRule>> rules_by_id;
-        HashMap<FlyString, Vector<MatchingRule>> rules_by_class;
-        HashMap<FlyString, Vector<MatchingRule>> rules_by_tag_name;
+        HashMap<DeprecatedFlyString, Vector<MatchingRule>> rules_by_id;
+        HashMap<DeprecatedFlyString, Vector<MatchingRule>> rules_by_class;
+        HashMap<DeprecatedFlyString, Vector<MatchingRule>> rules_by_tag_name;
         HashMap<Selector::PseudoElement, Vector<MatchingRule>> rules_by_pseudo_element;
         Vector<MatchingRule> other_rules;
     };
diff --git a/Userland/Libraries/LibWeb/DOM/ARIAMixin.cpp b/Userland/Libraries/LibWeb/DOM/ARIAMixin.cpp
index 04b472c31e0..2ea332026b7 100644
--- a/Userland/Libraries/LibWeb/DOM/ARIAMixin.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ARIAMixin.cpp
@@ -11,7 +11,7 @@
 namespace Web::DOM {
 
 // https://www.w3.org/TR/wai-aria-1.2/#introroles
-FlyString ARIAMixin::role_or_default() const
+DeprecatedFlyString ARIAMixin::role_or_default() const
 {
     // 1. Use the rules of the host language to detect that an element has a role attribute and to identify the attribute value string for it.
     auto role_string = role();
diff --git a/Userland/Libraries/LibWeb/DOM/ARIAMixin.h b/Userland/Libraries/LibWeb/DOM/ARIAMixin.h
index ec93ecb0366..4383af08482 100644
--- a/Userland/Libraries/LibWeb/DOM/ARIAMixin.h
+++ b/Userland/Libraries/LibWeb/DOM/ARIAMixin.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/WebIDL/ExceptionOr.h>
 
 namespace Web::DOM {
@@ -132,9 +132,9 @@ public:
     virtual WebIDL::ExceptionOr<void> set_aria_value_text(DeprecatedString const&) = 0;
 
     // https://www.w3.org/TR/html-aria/#docconformance
-    virtual FlyString default_role() const { return {}; };
+    virtual DeprecatedFlyString default_role() const { return {}; };
 
-    FlyString role_or_default() const;
+    DeprecatedFlyString role_or_default() const;
 
     // https://www.w3.org/TR/wai-aria-1.2/#tree_exclusion
     virtual bool exclude_from_accessibility_tree() const = 0;
diff --git a/Userland/Libraries/LibWeb/DOM/ARIARoleNames.cpp b/Userland/Libraries/LibWeb/DOM/ARIARoleNames.cpp
index afd709610e9..3d70ab243e7 100644
--- a/Userland/Libraries/LibWeb/DOM/ARIARoleNames.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ARIARoleNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::DOM::ARIARoleNames {
 
-#define __ENUMERATE_ARIA_ROLE(name) FlyString name;
+#define __ENUMERATE_ARIA_ROLE(name) DeprecatedFlyString name;
 ENUMERATE_ARIA_ROLES
 #undef __ENUMERATE_ARIA_ROLE
 
@@ -28,7 +28,7 @@ ENUMERATE_ARIA_ROLES
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#abstract_roles
-bool is_abstract_aria_role(FlyString const& role)
+bool is_abstract_aria_role(DeprecatedFlyString const& role)
 {
     return role.is_one_of(
         ARIARoleNames::command,
@@ -46,7 +46,7 @@ bool is_abstract_aria_role(FlyString const& role)
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#widget_roles
-bool is_widget_aria_role(FlyString const& role)
+bool is_widget_aria_role(DeprecatedFlyString const& role)
 {
     return role.to_lowercase().is_one_of(
         ARIARoleNames::button,
@@ -80,7 +80,7 @@ bool is_widget_aria_role(FlyString const& role)
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#document_structure_roles
-bool is_document_structure_aria_role(FlyString const& role)
+bool is_document_structure_aria_role(DeprecatedFlyString const& role)
 {
     return role.to_lowercase().is_one_of(
         ARIARoleNames::application,
@@ -123,7 +123,7 @@ bool is_document_structure_aria_role(FlyString const& role)
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#landmark_roles
-bool is_landmark_aria_role(FlyString const& role)
+bool is_landmark_aria_role(DeprecatedFlyString const& role)
 {
     return role.to_lowercase().is_one_of(
         ARIARoleNames::banner,
@@ -137,7 +137,7 @@ bool is_landmark_aria_role(FlyString const& role)
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#live_region_roles
-bool is_live_region_aria_role(FlyString const& role)
+bool is_live_region_aria_role(DeprecatedFlyString const& role)
 {
     return role.to_lowercase().is_one_of(
         ARIARoleNames::alert,
@@ -148,14 +148,14 @@ bool is_live_region_aria_role(FlyString const& role)
 }
 
 // https://www.w3.org/TR/wai-aria-1.2/#window_roles
-bool is_windows_aria_role(FlyString const& role)
+bool is_windows_aria_role(DeprecatedFlyString const& role)
 {
     return role.to_lowercase().is_one_of(
         ARIARoleNames::alertdialog,
         ARIARoleNames::dialog);
 }
 
-bool is_non_abstract_aria_role(FlyString const& role)
+bool is_non_abstract_aria_role(DeprecatedFlyString const& role)
 {
     return is_widget_aria_role(role)
         || is_document_structure_aria_role(role)
diff --git a/Userland/Libraries/LibWeb/DOM/ARIARoleNames.h b/Userland/Libraries/LibWeb/DOM/ARIARoleNames.h
index 36d310643e9..6bca60883d0 100644
--- a/Userland/Libraries/LibWeb/DOM/ARIARoleNames.h
+++ b/Userland/Libraries/LibWeb/DOM/ARIARoleNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::DOM::ARIARoleNames {
 
@@ -106,17 +106,17 @@ namespace Web::DOM::ARIARoleNames {
     __ENUMERATE_ARIA_ROLE(widget)           \
     __ENUMERATE_ARIA_ROLE(window)
 
-#define __ENUMERATE_ARIA_ROLE(name) extern FlyString name;
+#define __ENUMERATE_ARIA_ROLE(name) extern DeprecatedFlyString name;
 ENUMERATE_ARIA_ROLES
 #undef __ENUMERATE_ARIA_ROLE
 
-bool is_abstract_aria_role(FlyString const&);
-bool is_widget_aria_role(FlyString const&);
-bool is_document_structure_aria_role(FlyString const&);
-bool is_landmark_aria_role(FlyString const&);
-bool is_live_region_aria_role(FlyString const&);
-bool is_windows_aria_role(FlyString const&);
+bool is_abstract_aria_role(DeprecatedFlyString const&);
+bool is_widget_aria_role(DeprecatedFlyString const&);
+bool is_document_structure_aria_role(DeprecatedFlyString const&);
+bool is_landmark_aria_role(DeprecatedFlyString const&);
+bool is_live_region_aria_role(DeprecatedFlyString const&);
+bool is_windows_aria_role(DeprecatedFlyString const&);
 
-bool is_non_abstract_aria_role(FlyString const&);
+bool is_non_abstract_aria_role(DeprecatedFlyString const&);
 
 }
diff --git a/Userland/Libraries/LibWeb/DOM/Attr.cpp b/Userland/Libraries/LibWeb/DOM/Attr.cpp
index 4d6075b026c..b1c81848e6f 100644
--- a/Userland/Libraries/LibWeb/DOM/Attr.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Attr.cpp
@@ -13,7 +13,7 @@
 
 namespace Web::DOM {
 
-JS::NonnullGCPtr<Attr> Attr::create(Document& document, FlyString local_name, DeprecatedString value, Element const* owner_element)
+JS::NonnullGCPtr<Attr> Attr::create(Document& document, DeprecatedFlyString local_name, DeprecatedString value, Element const* owner_element)
 {
     return document.heap().allocate<Attr>(document.realm(), document, QualifiedName(move(local_name), {}, {}), move(value), owner_element);
 }
diff --git a/Userland/Libraries/LibWeb/DOM/Attr.h b/Userland/Libraries/LibWeb/DOM/Attr.h
index 5c48c99d4b7..3c88b7457c4 100644
--- a/Userland/Libraries/LibWeb/DOM/Attr.h
+++ b/Userland/Libraries/LibWeb/DOM/Attr.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/WeakPtr.h>
 #include <LibWeb/DOM/Node.h>
 #include <LibWeb/DOM/QualifiedName.h>
@@ -18,16 +18,16 @@ class Attr final : public Node {
     WEB_PLATFORM_OBJECT(Attr, Node);
 
 public:
-    static JS::NonnullGCPtr<Attr> create(Document&, FlyString local_name, DeprecatedString value, Element const* = nullptr);
+    static JS::NonnullGCPtr<Attr> create(Document&, DeprecatedFlyString local_name, DeprecatedString value, Element const* = nullptr);
     JS::NonnullGCPtr<Attr> clone(Document&);
 
     virtual ~Attr() override = default;
 
-    virtual FlyString node_name() const override { return name(); }
+    virtual DeprecatedFlyString node_name() const override { return name(); }
 
-    FlyString const& namespace_uri() const { return m_qualified_name.namespace_(); }
-    FlyString const& prefix() const { return m_qualified_name.prefix(); }
-    FlyString const& local_name() const { return m_qualified_name.local_name(); }
+    DeprecatedFlyString const& namespace_uri() const { return m_qualified_name.namespace_(); }
+    DeprecatedFlyString const& prefix() const { return m_qualified_name.prefix(); }
+    DeprecatedFlyString const& local_name() const { return m_qualified_name.local_name(); }
     DeprecatedString const& name() const { return m_qualified_name.as_string(); }
 
     DeprecatedString const& value() const { return m_value; }
diff --git a/Userland/Libraries/LibWeb/DOM/CDATASection.h b/Userland/Libraries/LibWeb/DOM/CDATASection.h
index 061b6aa48fa..819a506a8e6 100644
--- a/Userland/Libraries/LibWeb/DOM/CDATASection.h
+++ b/Userland/Libraries/LibWeb/DOM/CDATASection.h
@@ -18,7 +18,7 @@ public:
     virtual ~CDATASection() override;
 
     // ^Node
-    virtual FlyString node_name() const override { return "#cdata-section"; }
+    virtual DeprecatedFlyString node_name() const override { return "#cdata-section"; }
 
 private:
     CDATASection(Document&, DeprecatedString const&);
diff --git a/Userland/Libraries/LibWeb/DOM/Comment.h b/Userland/Libraries/LibWeb/DOM/Comment.h
index 3977501ad8a..0192c4a8f21 100644
--- a/Userland/Libraries/LibWeb/DOM/Comment.h
+++ b/Userland/Libraries/LibWeb/DOM/Comment.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/DOM/CharacterData.h>
 
 namespace Web::DOM {
@@ -18,7 +18,7 @@ public:
     static JS::NonnullGCPtr<Comment> construct_impl(JS::Realm&, DeprecatedString const& data);
     virtual ~Comment() override = default;
 
-    virtual FlyString node_name() const override { return "#comment"; }
+    virtual DeprecatedFlyString node_name() const override { return "#comment"; }
 
 private:
     Comment(Document&, DeprecatedString const&);
diff --git a/Userland/Libraries/LibWeb/DOM/CustomEvent.cpp b/Userland/Libraries/LibWeb/DOM/CustomEvent.cpp
index d271f08cf3c..9bc3b4c466e 100644
--- a/Userland/Libraries/LibWeb/DOM/CustomEvent.cpp
+++ b/Userland/Libraries/LibWeb/DOM/CustomEvent.cpp
@@ -11,17 +11,17 @@
 
 namespace Web::DOM {
 
-CustomEvent* CustomEvent::create(JS::Realm& realm, FlyString const& event_name, CustomEventInit const& event_init)
+CustomEvent* CustomEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, CustomEventInit const& event_init)
 {
     return realm.heap().allocate<CustomEvent>(realm, realm, event_name, event_init);
 }
 
-CustomEvent* CustomEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, CustomEventInit const& event_init)
+CustomEvent* CustomEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, CustomEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-CustomEvent::CustomEvent(JS::Realm& realm, FlyString const& event_name, CustomEventInit const& event_init)
+CustomEvent::CustomEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, CustomEventInit const& event_init)
     : Event(realm, event_name, event_init)
     , m_detail(event_init.detail)
 {
diff --git a/Userland/Libraries/LibWeb/DOM/CustomEvent.h b/Userland/Libraries/LibWeb/DOM/CustomEvent.h
index fa4d4851606..a42f917846a 100644
--- a/Userland/Libraries/LibWeb/DOM/CustomEvent.h
+++ b/Userland/Libraries/LibWeb/DOM/CustomEvent.h
@@ -20,8 +20,8 @@ class CustomEvent : public Event {
     WEB_PLATFORM_OBJECT(CustomEvent, Event);
 
 public:
-    static CustomEvent* create(JS::Realm&, FlyString const& event_name, CustomEventInit const& event_init = {});
-    static CustomEvent* construct_impl(JS::Realm&, FlyString const& event_name, CustomEventInit const& event_init);
+    static CustomEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, CustomEventInit const& event_init = {});
+    static CustomEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, CustomEventInit const& event_init);
 
     virtual ~CustomEvent() override;
 
@@ -33,7 +33,7 @@ public:
     void init_custom_event(DeprecatedString const& type, bool bubbles, bool cancelable, JS::Value detail);
 
 private:
-    CustomEvent(JS::Realm&, FlyString const& event_name, CustomEventInit const& event_init);
+    CustomEvent(JS::Realm&, DeprecatedFlyString const& event_name, CustomEventInit const& event_init);
 
     // https://dom.spec.whatwg.org/#dom-customevent-initcustomevent-type-bubbles-cancelable-detail-detail
     JS::Value m_detail { JS::js_null() };
diff --git a/Userland/Libraries/LibWeb/DOM/DOMEventListener.h b/Userland/Libraries/LibWeb/DOM/DOMEventListener.h
index 87a3b744a8d..3d944f95e29 100644
--- a/Userland/Libraries/LibWeb/DOM/DOMEventListener.h
+++ b/Userland/Libraries/LibWeb/DOM/DOMEventListener.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Heap/GCPtr.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibWeb/Forward.h>
@@ -21,7 +21,7 @@ public:
     ~DOMEventListener();
 
     // type (a string)
-    FlyString type;
+    DeprecatedFlyString type;
 
     // callback (null or an EventListener object)
     JS::GCPtr<IDLEventListener> callback;
diff --git a/Userland/Libraries/LibWeb/DOM/DOMTokenList.cpp b/Userland/Libraries/LibWeb/DOM/DOMTokenList.cpp
index 8806e05fa3f..768dc3fa57a 100644
--- a/Userland/Libraries/LibWeb/DOM/DOMTokenList.cpp
+++ b/Userland/Libraries/LibWeb/DOM/DOMTokenList.cpp
@@ -52,14 +52,14 @@ inline void replace_in_ordered_set(Vector<DeprecatedString>& set, StringView ite
 
 namespace Web::DOM {
 
-DOMTokenList* DOMTokenList::create(Element const& associated_element, FlyString associated_attribute)
+DOMTokenList* DOMTokenList::create(Element const& associated_element, DeprecatedFlyString associated_attribute)
 {
     auto& realm = associated_element.realm();
     return realm.heap().allocate<DOMTokenList>(realm, associated_element, move(associated_attribute));
 }
 
 // https://dom.spec.whatwg.org/#ref-for-domtokenlist%E2%91%A0%E2%91%A2
-DOMTokenList::DOMTokenList(Element const& associated_element, FlyString associated_attribute)
+DOMTokenList::DOMTokenList(Element const& associated_element, DeprecatedFlyString associated_attribute)
     : Bindings::LegacyPlatformObject(Bindings::cached_web_prototype(associated_element.realm(), "DOMTokenList"))
     , m_associated_element(associated_element)
     , m_associated_attribute(move(associated_attribute))
diff --git a/Userland/Libraries/LibWeb/DOM/DOMTokenList.h b/Userland/Libraries/LibWeb/DOM/DOMTokenList.h
index 40b3704d356..4be3d0a2b72 100644
--- a/Userland/Libraries/LibWeb/DOM/DOMTokenList.h
+++ b/Userland/Libraries/LibWeb/DOM/DOMTokenList.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Optional.h>
 #include <AK/StringView.h>
 #include <AK/Vector.h>
@@ -23,7 +23,7 @@ class DOMTokenList final : public Bindings::LegacyPlatformObject {
     WEB_PLATFORM_OBJECT(DOMTokenList, Bindings::LegacyPlatformObject);
 
 public:
-    static DOMTokenList* create(Element const& associated_element, FlyString associated_attribute);
+    static DOMTokenList* create(Element const& associated_element, DeprecatedFlyString associated_attribute);
     ~DOMTokenList() = default;
 
     void associated_attribute_changed(StringView value);
@@ -43,7 +43,7 @@ public:
     void set_value(DeprecatedString value);
 
 private:
-    DOMTokenList(Element const& associated_element, FlyString associated_attribute);
+    DOMTokenList(Element const& associated_element, DeprecatedFlyString associated_attribute);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
@@ -51,7 +51,7 @@ private:
     void run_update_steps();
 
     JS::NonnullGCPtr<Element> m_associated_element;
-    FlyString m_associated_attribute;
+    DeprecatedFlyString m_associated_attribute;
     Vector<DeprecatedString> m_token_set;
 };
 
diff --git a/Userland/Libraries/LibWeb/DOM/Document.cpp b/Userland/Libraries/LibWeb/DOM/Document.cpp
index 8c9b24b2472..8c4d0abad84 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Document.cpp
@@ -1018,9 +1018,9 @@ JS::NonnullGCPtr<HTMLCollection> Document::get_elements_by_name(DeprecatedString
     });
 }
 
-JS::NonnullGCPtr<HTMLCollection> Document::get_elements_by_class_name(FlyString const& class_names)
+JS::NonnullGCPtr<HTMLCollection> Document::get_elements_by_class_name(DeprecatedFlyString const& class_names)
 {
-    Vector<FlyString> list_of_class_names;
+    Vector<DeprecatedFlyString> list_of_class_names;
     for (auto& name : class_names.view().split_view(' ')) {
         list_of_class_names.append(name);
     }
@@ -1180,7 +1180,7 @@ JS::Value Document::run_javascript(StringView source, StringView filename)
 }
 
 // https://dom.spec.whatwg.org/#dom-document-createelement
-WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> Document::create_element(FlyString const& a_local_name)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> Document::create_element(DeprecatedFlyString const& a_local_name)
 {
     auto local_name = a_local_name;
 
@@ -1196,7 +1196,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> Document::create_element(FlyStrin
     // FIXME: 4. If options is a dictionary and options["is"] exists, then set is to it.
 
     // 5. Let namespace be the HTML namespace, if this is an HTML document or this’s content type is "application/xhtml+xml"; otherwise null.
-    FlyString namespace_;
+    DeprecatedFlyString namespace_;
     if (document_type() == Type::HTML || content_type() == "application/xhtml+xml"sv)
         namespace_ = Namespace::HTML;
 
diff --git a/Userland/Libraries/LibWeb/DOM/Document.h b/Userland/Libraries/LibWeb/DOM/Document.h
index 2278959b61d..5757519dd41 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.h
+++ b/Userland/Libraries/LibWeb/DOM/Document.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/NonnullRefPtrVector.h>
@@ -127,7 +127,7 @@ public:
 
     CSS::StyleSheetList* style_sheets_for_bindings() { return &style_sheets(); }
 
-    virtual FlyString node_name() const override { return "#document"; }
+    virtual DeprecatedFlyString node_name() const override { return "#document"; }
 
     void set_hovered_node(Node*);
     Node* hovered_node() { return m_hovered_node.ptr(); }
@@ -203,7 +203,7 @@ public:
     void schedule_layout_update();
 
     JS::NonnullGCPtr<HTMLCollection> get_elements_by_name(DeprecatedString const&);
-    JS::NonnullGCPtr<HTMLCollection> get_elements_by_class_name(FlyString const&);
+    JS::NonnullGCPtr<HTMLCollection> get_elements_by_class_name(DeprecatedFlyString const&);
 
     JS::NonnullGCPtr<HTMLCollection> applets();
     JS::NonnullGCPtr<HTMLCollection> anchors();
@@ -222,7 +222,7 @@ public:
 
     JS::Value run_javascript(StringView source, StringView filename = "(unknown)"sv);
 
-    WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> create_element(FlyString const& local_name);
+    WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> create_element(DeprecatedFlyString const& local_name);
     WebIDL::ExceptionOr<JS::NonnullGCPtr<Element>> create_element_ns(DeprecatedString const& namespace_, DeprecatedString const& qualified_name);
     JS::NonnullGCPtr<DocumentFragment> create_document_fragment();
     JS::NonnullGCPtr<Text> create_text_node(DeprecatedString const& data);
@@ -371,8 +371,8 @@ public:
     static bool is_valid_name(DeprecatedString const&);
 
     struct PrefixAndTagName {
-        FlyString prefix;
-        FlyString tag_name;
+        DeprecatedFlyString prefix;
+        DeprecatedFlyString tag_name;
     };
     static WebIDL::ExceptionOr<PrefixAndTagName> validate_qualified_name(JS::Realm&, DeprecatedString const& qualified_name);
 
@@ -456,7 +456,7 @@ private:
     Document(JS::Realm&, AK::URL const&);
 
     // ^HTML::GlobalEventHandlers
-    virtual EventTarget& global_event_handlers_to_event_target(FlyString const&) final { return *this; }
+    virtual EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const&) final { return *this; }
 
     void tear_down_layout_tree();
 
diff --git a/Userland/Libraries/LibWeb/DOM/DocumentFragment.h b/Userland/Libraries/LibWeb/DOM/DocumentFragment.h
index e0c5213d424..47116712a82 100644
--- a/Userland/Libraries/LibWeb/DOM/DocumentFragment.h
+++ b/Userland/Libraries/LibWeb/DOM/DocumentFragment.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/DOM/Element.h>
 #include <LibWeb/DOM/NonElementParentNode.h>
 #include <LibWeb/DOM/ParentNode.h>
@@ -23,7 +23,7 @@ public:
 
     virtual ~DocumentFragment() override = default;
 
-    virtual FlyString node_name() const override { return "#document-fragment"; }
+    virtual DeprecatedFlyString node_name() const override { return "#document-fragment"; }
 
     Element* host() { return m_host.ptr(); }
     Element const* host() const { return m_host.ptr(); }
diff --git a/Userland/Libraries/LibWeb/DOM/DocumentType.h b/Userland/Libraries/LibWeb/DOM/DocumentType.h
index 1ef8040c937..deb8b96a374 100644
--- a/Userland/Libraries/LibWeb/DOM/DocumentType.h
+++ b/Userland/Libraries/LibWeb/DOM/DocumentType.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/DOM/ChildNode.h>
 #include <LibWeb/DOM/Node.h>
 
@@ -22,7 +22,7 @@ public:
 
     virtual ~DocumentType() override = default;
 
-    virtual FlyString node_name() const override { return "#doctype"; }
+    virtual DeprecatedFlyString node_name() const override { return "#doctype"; }
 
     DeprecatedString const& name() const { return m_name; }
     void set_name(DeprecatedString const& name) { m_name = name; }
diff --git a/Userland/Libraries/LibWeb/DOM/Element.cpp b/Userland/Libraries/LibWeb/DOM/Element.cpp
index a7c4e4b085c..135e27f3c9f 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Element.cpp
@@ -80,7 +80,7 @@ void Element::visit_edges(Cell::Visitor& visitor)
 }
 
 // https://dom.spec.whatwg.org/#dom-element-getattribute
-DeprecatedString Element::get_attribute(FlyString const& name) const
+DeprecatedString Element::get_attribute(DeprecatedFlyString const& name) const
 {
     // 1. Let attr be the result of getting an attribute given qualifiedName and this.
     auto const* attribute = m_attributes->get_attribute(name);
@@ -94,14 +94,14 @@ DeprecatedString Element::get_attribute(FlyString const& name) const
 }
 
 // https://dom.spec.whatwg.org/#dom-element-getattributenode
-JS::GCPtr<Attr> Element::get_attribute_node(FlyString const& name) const
+JS::GCPtr<Attr> Element::get_attribute_node(DeprecatedFlyString const& name) const
 {
     // The getAttributeNode(qualifiedName) method steps are to return the result of getting an attribute given qualifiedName and this.
     return m_attributes->get_attribute(name);
 }
 
 // https://dom.spec.whatwg.org/#dom-element-setattribute
-WebIDL::ExceptionOr<void> Element::set_attribute(FlyString const& name, DeprecatedString const& value)
+WebIDL::ExceptionOr<void> Element::set_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     // 1. If qualifiedName does not match the Name production in XML, then throw an "InvalidCharacterError" DOMException.
     // FIXME: Proper name validation
@@ -136,7 +136,7 @@ WebIDL::ExceptionOr<void> Element::set_attribute(FlyString const& name, Deprecat
 }
 
 // https://dom.spec.whatwg.org/#validate-and-extract
-WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm& realm, FlyString namespace_, FlyString qualified_name)
+WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm& realm, DeprecatedFlyString namespace_, DeprecatedFlyString qualified_name)
 {
     // 1. If namespace is the empty string, then set it to null.
     if (namespace_.is_empty())
@@ -146,7 +146,7 @@ WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm& realm, FlyStr
     TRY(Document::validate_qualified_name(realm, qualified_name));
 
     // 3. Let prefix be null.
-    FlyString prefix = {};
+    DeprecatedFlyString prefix = {};
 
     // 4. Let localName be qualifiedName.
     auto local_name = qualified_name;
@@ -179,7 +179,7 @@ WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm& realm, FlyStr
 }
 
 // https://dom.spec.whatwg.org/#dom-element-setattributens
-WebIDL::ExceptionOr<void> Element::set_attribute_ns(FlyString const& namespace_, FlyString const& qualified_name, DeprecatedString const& value)
+WebIDL::ExceptionOr<void> Element::set_attribute_ns(DeprecatedFlyString const& namespace_, DeprecatedFlyString const& qualified_name, DeprecatedString const& value)
 {
     // 1. Let namespace, prefix, and localName be the result of passing namespace and qualifiedName to validate and extract.
     auto extracted_qualified_name = TRY(validate_and_extract(realm(), namespace_, qualified_name));
@@ -191,7 +191,7 @@ WebIDL::ExceptionOr<void> Element::set_attribute_ns(FlyString const& namespace_,
 }
 
 // https://dom.spec.whatwg.org/#dom-element-removeattribute
-void Element::remove_attribute(FlyString const& name)
+void Element::remove_attribute(DeprecatedFlyString const& name)
 {
     m_attributes->remove_attribute(name);
 
@@ -201,13 +201,13 @@ void Element::remove_attribute(FlyString const& name)
 }
 
 // https://dom.spec.whatwg.org/#dom-element-hasattribute
-bool Element::has_attribute(FlyString const& name) const
+bool Element::has_attribute(DeprecatedFlyString const& name) const
 {
     return m_attributes->get_attribute(name) != nullptr;
 }
 
 // https://dom.spec.whatwg.org/#dom-element-toggleattribute
-WebIDL::ExceptionOr<bool> Element::toggle_attribute(FlyString const& name, Optional<bool> force)
+WebIDL::ExceptionOr<bool> Element::toggle_attribute(DeprecatedFlyString const& name, Optional<bool> force)
 {
     // 1. If qualifiedName does not match the Name production in XML, then throw an "InvalidCharacterError" DOMException.
     // FIXME: Proper name validation
@@ -264,7 +264,7 @@ Vector<DeprecatedString> Element::get_attribute_names() const
     return names;
 }
 
-bool Element::has_class(FlyString const& class_name, CaseSensitivity case_sensitivity) const
+bool Element::has_class(DeprecatedFlyString const& class_name, CaseSensitivity case_sensitivity) const
 {
     if (case_sensitivity == CaseSensitivity::CaseSensitive) {
         return any_of(m_classes, [&](auto& it) {
@@ -330,7 +330,7 @@ CSS::CSSStyleDeclaration const* Element::inline_style() const
     return m_inline_style.ptr();
 }
 
-void Element::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void Element::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     if (name == HTML::AttributeNames::class_) {
         auto new_classes = value.split_view(Infra::is_ascii_whitespace);
@@ -350,7 +350,7 @@ void Element::parse_attribute(FlyString const& name, DeprecatedString const& val
     }
 }
 
-void Element::did_remove_attribute(FlyString const& name)
+void Element::did_remove_attribute(DeprecatedFlyString const& name)
 {
     if (name == HTML::AttributeNames::style) {
         if (m_inline_style) {
@@ -516,9 +516,9 @@ bool Element::is_active() const
     return document().active_element() == this;
 }
 
-JS::NonnullGCPtr<HTMLCollection> Element::get_elements_by_class_name(FlyString const& class_names)
+JS::NonnullGCPtr<HTMLCollection> Element::get_elements_by_class_name(DeprecatedFlyString const& class_names)
 {
-    Vector<FlyString> list_of_class_names;
+    Vector<DeprecatedFlyString> list_of_class_names;
     for (auto& name : class_names.view().split_view_if(Infra::is_ascii_whitespace)) {
         list_of_class_names.append(name);
     }
@@ -1258,7 +1258,7 @@ ErrorOr<void> Element::scroll_into_view(Optional<Variant<bool, ScrollIntoViewOpt
     // FIXME: 8. Optionally perform some other action that brings the element to the user’s attention.
 }
 
-void Element::invalidate_style_after_attribute_change(FlyString const& attribute_name)
+void Element::invalidate_style_after_attribute_change(DeprecatedFlyString const& attribute_name)
 {
     // FIXME: Only invalidate if the attribute can actually affect style.
     (void)attribute_name;
diff --git a/Userland/Libraries/LibWeb/DOM/Element.h b/Userland/Libraries/LibWeb/DOM/Element.h
index 1792a32fc7a..ed95dda952a 100644
--- a/Userland/Libraries/LibWeb/DOM/Element.h
+++ b/Userland/Libraries/LibWeb/DOM/Element.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <LibWeb/Bindings/ElementPrototype.h>
 #include <LibWeb/CSS/CSSStyleDeclaration.h>
 #include <LibWeb/CSS/StyleComputer.h>
@@ -50,31 +50,31 @@ public:
 
     DeprecatedString const& qualified_name() const { return m_qualified_name.as_string(); }
     DeprecatedString const& html_uppercased_qualified_name() const { return m_html_uppercased_qualified_name; }
-    virtual FlyString node_name() const final { return html_uppercased_qualified_name(); }
-    FlyString const& local_name() const { return m_qualified_name.local_name(); }
+    virtual DeprecatedFlyString node_name() const final { return html_uppercased_qualified_name(); }
+    DeprecatedFlyString const& local_name() const { return m_qualified_name.local_name(); }
 
     // NOTE: This is for the JS bindings
     DeprecatedString const& tag_name() const { return html_uppercased_qualified_name(); }
 
-    FlyString const& prefix() const { return m_qualified_name.prefix(); }
-    FlyString const& namespace_() const { return m_qualified_name.namespace_(); }
+    DeprecatedFlyString const& prefix() const { return m_qualified_name.prefix(); }
+    DeprecatedFlyString const& namespace_() const { return m_qualified_name.namespace_(); }
 
     // NOTE: This is for the JS bindings
-    FlyString const& namespace_uri() const { return namespace_(); }
+    DeprecatedFlyString const& namespace_uri() const { return namespace_(); }
 
-    bool has_attribute(FlyString const& name) const;
+    bool has_attribute(DeprecatedFlyString const& name) const;
     bool has_attributes() const { return !m_attributes->is_empty(); }
-    DeprecatedString attribute(FlyString const& name) const { return get_attribute(name); }
-    DeprecatedString get_attribute(FlyString const& name) const;
-    WebIDL::ExceptionOr<void> set_attribute(FlyString const& name, DeprecatedString const& value);
-    WebIDL::ExceptionOr<void> set_attribute_ns(FlyString const& namespace_, FlyString const& qualified_name, DeprecatedString const& value);
-    void remove_attribute(FlyString const& name);
-    WebIDL::ExceptionOr<bool> toggle_attribute(FlyString const& name, Optional<bool> force);
+    DeprecatedString attribute(DeprecatedFlyString const& name) const { return get_attribute(name); }
+    DeprecatedString get_attribute(DeprecatedFlyString const& name) const;
+    WebIDL::ExceptionOr<void> set_attribute(DeprecatedFlyString const& name, DeprecatedString const& value);
+    WebIDL::ExceptionOr<void> set_attribute_ns(DeprecatedFlyString const& namespace_, DeprecatedFlyString const& qualified_name, DeprecatedString const& value);
+    void remove_attribute(DeprecatedFlyString const& name);
+    WebIDL::ExceptionOr<bool> toggle_attribute(DeprecatedFlyString const& name, Optional<bool> force);
     size_t attribute_list_size() const { return m_attributes->length(); }
     NamedNodeMap const* attributes() const { return m_attributes.ptr(); }
     Vector<DeprecatedString> get_attribute_names() const;
 
-    JS::GCPtr<Attr> get_attribute_node(FlyString const& name) const;
+    JS::GCPtr<Attr> get_attribute_node(DeprecatedFlyString const& name) const;
 
     DOMTokenList* class_list();
 
@@ -95,12 +95,12 @@ public:
         }
     }
 
-    bool has_class(FlyString const&, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
-    Vector<FlyString> const& class_names() const { return m_classes; }
+    bool has_class(DeprecatedFlyString const&, CaseSensitivity = CaseSensitivity::CaseSensitive) const;
+    Vector<DeprecatedFlyString> const& class_names() const { return m_classes; }
 
     virtual void apply_presentational_hints(CSS::StyleProperties&) const { }
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value);
-    virtual void did_remove_attribute(FlyString const&);
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value);
+    virtual void did_remove_attribute(DeprecatedFlyString const&);
 
     enum class NeedsRelayout {
         No = 0,
@@ -129,14 +129,14 @@ public:
     bool is_focused() const;
     bool is_active() const;
 
-    JS::NonnullGCPtr<HTMLCollection> get_elements_by_class_name(FlyString const&);
+    JS::NonnullGCPtr<HTMLCollection> get_elements_by_class_name(DeprecatedFlyString const&);
 
     ShadowRoot* shadow_root() { return m_shadow_root.ptr(); }
     ShadowRoot const* shadow_root() const { return m_shadow_root.ptr(); }
     void set_shadow_root(JS::GCPtr<ShadowRoot>);
 
-    void set_custom_properties(HashMap<FlyString, CSS::StyleProperty> custom_properties) { m_custom_properties = move(custom_properties); }
-    HashMap<FlyString, CSS::StyleProperty> const& custom_properties() const { return m_custom_properties; }
+    void set_custom_properties(HashMap<DeprecatedFlyString, CSS::StyleProperty> custom_properties) { m_custom_properties = move(custom_properties); }
+    HashMap<DeprecatedFlyString, CSS::StyleProperty> const& custom_properties() const { return m_custom_properties; }
 
     void queue_an_element_task(HTML::Task::Source, JS::SafeFunction<void()>);
 
@@ -261,7 +261,7 @@ protected:
 private:
     void make_html_uppercased_qualified_name();
 
-    void invalidate_style_after_attribute_change(FlyString const& attribute_name);
+    void invalidate_style_after_attribute_change(DeprecatedFlyString const& attribute_name);
 
     WebIDL::ExceptionOr<JS::GCPtr<Node>> insert_adjacent(DeprecatedString const& where, JS::NonnullGCPtr<Node> node);
 
@@ -274,9 +274,9 @@ private:
     JS::GCPtr<ShadowRoot> m_shadow_root;
 
     RefPtr<CSS::StyleProperties> m_computed_css_values;
-    HashMap<FlyString, CSS::StyleProperty> m_custom_properties;
+    HashMap<DeprecatedFlyString, CSS::StyleProperty> m_custom_properties;
 
-    Vector<FlyString> m_classes;
+    Vector<DeprecatedFlyString> m_classes;
 
     Array<JS::GCPtr<Layout::Node>, to_underlying(CSS::Selector::PseudoElement::PseudoElementCount)> m_pseudo_element_nodes;
 };
@@ -284,6 +284,6 @@ private:
 template<>
 inline bool Node::fast_is<Element>() const { return is_element(); }
 
-WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm&, FlyString namespace_, FlyString qualified_name);
+WebIDL::ExceptionOr<QualifiedName> validate_and_extract(JS::Realm&, DeprecatedFlyString namespace_, DeprecatedFlyString qualified_name);
 
 }
diff --git a/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp b/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
index 617d24f8aa9..1b8bab27326 100644
--- a/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ElementFactory.cpp
@@ -95,7 +95,7 @@
 namespace Web::DOM {
 
 // https://dom.spec.whatwg.org/#concept-create-element
-JS::NonnullGCPtr<Element> create_element(Document& document, FlyString local_name, FlyString namespace_, FlyString prefix)
+JS::NonnullGCPtr<Element> create_element(Document& document, DeprecatedFlyString local_name, DeprecatedFlyString namespace_, DeprecatedFlyString prefix)
 {
     // 1. If prefix was not given, let prefix be null.
     // NOTE: This is already taken care of by `prefix` having a default value.
diff --git a/Userland/Libraries/LibWeb/DOM/ElementFactory.h b/Userland/Libraries/LibWeb/DOM/ElementFactory.h
index 3c9ac81cbb1..ff2d46334ae 100644
--- a/Userland/Libraries/LibWeb/DOM/ElementFactory.h
+++ b/Userland/Libraries/LibWeb/DOM/ElementFactory.h
@@ -10,6 +10,6 @@
 
 namespace Web::DOM {
 
-JS::NonnullGCPtr<Element> create_element(Document&, FlyString local_name, FlyString namespace_, FlyString prefix = {});
+JS::NonnullGCPtr<Element> create_element(Document&, DeprecatedFlyString local_name, DeprecatedFlyString namespace_, DeprecatedFlyString prefix = {});
 
 }
diff --git a/Userland/Libraries/LibWeb/DOM/Event.cpp b/Userland/Libraries/LibWeb/DOM/Event.cpp
index 752f1ec0bba..a42a587e52c 100644
--- a/Userland/Libraries/LibWeb/DOM/Event.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Event.cpp
@@ -14,24 +14,24 @@
 
 namespace Web::DOM {
 
-JS::NonnullGCPtr<Event> Event::create(JS::Realm& realm, FlyString const& event_name, EventInit const& event_init)
+JS::NonnullGCPtr<Event> Event::create(JS::Realm& realm, DeprecatedFlyString const& event_name, EventInit const& event_init)
 {
     return realm.heap().allocate<Event>(realm, realm, event_name, event_init);
 }
 
-JS::NonnullGCPtr<Event> Event::construct_impl(JS::Realm& realm, FlyString const& event_name, EventInit const& event_init)
+JS::NonnullGCPtr<Event> Event::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, EventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-Event::Event(JS::Realm& realm, FlyString const& type)
+Event::Event(JS::Realm& realm, DeprecatedFlyString const& type)
     : PlatformObject(Bindings::cached_web_prototype(realm, "Event"))
     , m_type(type)
     , m_initialized(true)
 {
 }
 
-Event::Event(JS::Realm& realm, FlyString const& type, EventInit const& event_init)
+Event::Event(JS::Realm& realm, DeprecatedFlyString const& type, EventInit const& event_init)
     : PlatformObject(Bindings::cached_web_prototype(realm, "Event"))
     , m_type(type)
     , m_bubbles(event_init.bubbles)
diff --git a/Userland/Libraries/LibWeb/DOM/Event.h b/Userland/Libraries/LibWeb/DOM/Event.h
index a7871e73cd5..53b8f3279cd 100644
--- a/Userland/Libraries/LibWeb/DOM/Event.h
+++ b/Userland/Libraries/LibWeb/DOM/Event.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/Bindings/PlatformObject.h>
 #include <LibWeb/DOM/EventTarget.h>
 
@@ -45,17 +45,17 @@ public:
 
     using Path = Vector<PathEntry>;
 
-    static JS::NonnullGCPtr<Event> create(JS::Realm&, FlyString const& event_name, EventInit const& event_init = {});
-    static JS::NonnullGCPtr<Event> construct_impl(JS::Realm&, FlyString const& event_name, EventInit const& event_init);
+    static JS::NonnullGCPtr<Event> create(JS::Realm&, DeprecatedFlyString const& event_name, EventInit const& event_init = {});
+    static JS::NonnullGCPtr<Event> construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, EventInit const& event_init);
 
-    Event(JS::Realm&, FlyString const& type);
-    Event(JS::Realm&, FlyString const& type, EventInit const& event_init);
+    Event(JS::Realm&, DeprecatedFlyString const& type);
+    Event(JS::Realm&, DeprecatedFlyString const& type, EventInit const& event_init);
 
     virtual ~Event() = default;
 
     double time_stamp() const;
 
-    FlyString const& type() const { return m_type; }
+    DeprecatedFlyString const& type() const { return m_type; }
     void set_type(StringView type) { m_type = type; }
 
     JS::GCPtr<EventTarget> target() const { return m_target; }
@@ -148,7 +148,7 @@ protected:
     virtual void visit_edges(Visitor&) override;
 
 private:
-    FlyString m_type;
+    DeprecatedFlyString m_type;
     JS::GCPtr<EventTarget> m_target;
     JS::GCPtr<EventTarget> m_related_target;
     JS::GCPtr<EventTarget> m_current_target;
diff --git a/Userland/Libraries/LibWeb/DOM/EventTarget.cpp b/Userland/Libraries/LibWeb/DOM/EventTarget.cpp
index 45a7fea65b5..cd2a6256fc8 100644
--- a/Userland/Libraries/LibWeb/DOM/EventTarget.cpp
+++ b/Userland/Libraries/LibWeb/DOM/EventTarget.cpp
@@ -120,7 +120,7 @@ static FlattenedAddEventListenerOptions flatten_add_event_listener_options(Varia
 }
 
 // https://dom.spec.whatwg.org/#dom-eventtarget-addeventlistener
-void EventTarget::add_event_listener(FlyString const& type, IDLEventListener* callback, Variant<AddEventListenerOptions, bool> const& options)
+void EventTarget::add_event_listener(DeprecatedFlyString const& type, IDLEventListener* callback, Variant<AddEventListenerOptions, bool> const& options)
 {
     // 1. Let capture, passive, once, and signal be the result of flattening more options.
     auto flattened_options = flatten_add_event_listener_options(options);
@@ -138,7 +138,7 @@ void EventTarget::add_event_listener(FlyString const& type, IDLEventListener* ca
     add_an_event_listener(*event_listener);
 }
 
-void EventTarget::add_event_listener_without_options(FlyString const& type, IDLEventListener& callback)
+void EventTarget::add_event_listener_without_options(DeprecatedFlyString const& type, IDLEventListener& callback)
 {
     add_event_listener(type, &callback, AddEventListenerOptions {});
 }
@@ -179,7 +179,7 @@ void EventTarget::add_an_event_listener(DOMEventListener& listener)
 }
 
 // https://dom.spec.whatwg.org/#dom-eventtarget-removeeventlistener
-void EventTarget::remove_event_listener(FlyString const& type, IDLEventListener* callback, Variant<EventListenerOptions, bool> const& options)
+void EventTarget::remove_event_listener(DeprecatedFlyString const& type, IDLEventListener* callback, Variant<EventListenerOptions, bool> const& options)
 {
     // 1. Let capture be the result of flattening options.
     bool capture = flatten_event_listener_options(options);
@@ -202,7 +202,7 @@ void EventTarget::remove_event_listener(FlyString const& type, IDLEventListener*
         remove_an_event_listener(**it);
 }
 
-void EventTarget::remove_event_listener_without_options(FlyString const& type, IDLEventListener& callback)
+void EventTarget::remove_event_listener_without_options(DeprecatedFlyString const& type, IDLEventListener& callback)
 {
     remove_event_listener(type, &callback, EventListenerOptions {});
 }
@@ -241,7 +241,7 @@ WebIDL::ExceptionOr<bool> EventTarget::dispatch_event_binding(Event& event)
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#window-reflecting-body-element-event-handler-set
-bool is_window_reflecting_body_element_event_handler(FlyString const& name)
+bool is_window_reflecting_body_element_event_handler(DeprecatedFlyString const& name)
 {
     return name.is_one_of(
         HTML::EventNames::blur,
@@ -253,7 +253,7 @@ bool is_window_reflecting_body_element_event_handler(FlyString const& name)
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#windoweventhandlers
-static bool is_window_event_handler(FlyString const& name)
+static bool is_window_event_handler(DeprecatedFlyString const& name)
 {
     return name.is_one_of(
         HTML::EventNames::afterprint,
@@ -275,7 +275,7 @@ static bool is_window_event_handler(FlyString const& name)
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#determining-the-target-of-an-event-handler
-static EventTarget* determine_target_of_event_handler(EventTarget& event_target, FlyString const& name)
+static EventTarget* determine_target_of_event_handler(EventTarget& event_target, DeprecatedFlyString const& name)
 {
     // To determine the target of an event handler, given an EventTarget object eventTarget on which the event handler is exposed,
     // and an event handler name name, the following steps are taken:
@@ -300,7 +300,7 @@ static EventTarget* determine_target_of_event_handler(EventTarget& event_target,
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-attributes:event-handler-idl-attributes-2
-WebIDL::CallbackType* EventTarget::event_handler_attribute(FlyString const& name)
+WebIDL::CallbackType* EventTarget::event_handler_attribute(DeprecatedFlyString const& name)
 {
     // 1. Let eventTarget be the result of determining the target of an event handler given this object and name.
     auto target = determine_target_of_event_handler(*this, name);
@@ -314,7 +314,7 @@ WebIDL::CallbackType* EventTarget::event_handler_attribute(FlyString const& name
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#getting-the-current-value-of-the-event-handler
-WebIDL::CallbackType* EventTarget::get_current_value_of_event_handler(FlyString const& name)
+WebIDL::CallbackType* EventTarget::get_current_value_of_event_handler(DeprecatedFlyString const& name)
 {
     // 1. Let handlerMap be eventTarget's event handler map. (NOTE: Not necessary)
 
@@ -473,7 +473,7 @@ WebIDL::CallbackType* EventTarget::get_current_value_of_event_handler(FlyString
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-attributes:event-handler-idl-attributes-3
-void EventTarget::set_event_handler_attribute(FlyString const& name, WebIDL::CallbackType* value)
+void EventTarget::set_event_handler_attribute(DeprecatedFlyString const& name, WebIDL::CallbackType* value)
 {
     // 1. Let eventTarget be the result of determining the target of an event handler given this object and name.
     auto event_target = determine_target_of_event_handler(*this, name);
@@ -520,7 +520,7 @@ void EventTarget::set_event_handler_attribute(FlyString const& name, WebIDL::Cal
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#activate-an-event-handler
-void EventTarget::activate_event_handler(FlyString const& name, HTML::EventHandler& event_handler)
+void EventTarget::activate_event_handler(DeprecatedFlyString const& name, HTML::EventHandler& event_handler)
 {
     // 1. Let handlerMap be eventTarget's event handler map.
     // 2. Let eventHandler be handlerMap[name].
@@ -570,7 +570,7 @@ void EventTarget::activate_event_handler(FlyString const& name, HTML::EventHandl
     event_handler.listener = listener;
 }
 
-void EventTarget::deactivate_event_handler(FlyString const& name)
+void EventTarget::deactivate_event_handler(DeprecatedFlyString const& name)
 {
     // 1. Let handlerMap be eventTarget's event handler map. (NOTE: Not necessary)
 
@@ -600,7 +600,7 @@ void EventTarget::deactivate_event_handler(FlyString const& name)
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#the-event-handler-processing-algorithm
-JS::ThrowCompletionOr<void> EventTarget::process_event_handler_for_event(FlyString const& name, Event& event)
+JS::ThrowCompletionOr<void> EventTarget::process_event_handler_for_event(DeprecatedFlyString const& name, Event& event)
 {
     // 1. Let callback be the result of getting the current value of the event handler given eventTarget and name.
     auto* callback = get_current_value_of_event_handler(name);
@@ -679,7 +679,7 @@ JS::ThrowCompletionOr<void> EventTarget::process_event_handler_for_event(FlyStri
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-attributes:concept-element-attributes-change-ext
-void EventTarget::element_event_handler_attribute_changed(FlyString const& local_name, DeprecatedString const& value)
+void EventTarget::element_event_handler_attribute_changed(DeprecatedFlyString const& local_name, DeprecatedString const& value)
 {
     // NOTE: Step 1 of this algorithm was handled in HTMLElement::parse_attribute.
 
@@ -735,7 +735,7 @@ bool EventTarget::dispatch_event(Event& event)
     return EventDispatcher::dispatch(*this, event);
 }
 
-bool EventTarget::has_event_listener(FlyString const& type) const
+bool EventTarget::has_event_listener(DeprecatedFlyString const& type) const
 {
     for (auto& listener : m_event_listener_list) {
         if (listener->type == type)
diff --git a/Userland/Libraries/LibWeb/DOM/EventTarget.h b/Userland/Libraries/LibWeb/DOM/EventTarget.h
index a818733db8f..240d9ad3878 100644
--- a/Userland/Libraries/LibWeb/DOM/EventTarget.h
+++ b/Userland/Libraries/LibWeb/DOM/EventTarget.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Noncopyable.h>
 #include <AK/Vector.h>
 #include <LibJS/Forward.h>
@@ -26,12 +26,12 @@ public:
 
     virtual bool is_focusable() const { return false; }
 
-    void add_event_listener(FlyString const& type, IDLEventListener* callback, Variant<AddEventListenerOptions, bool> const& options);
-    void remove_event_listener(FlyString const& type, IDLEventListener* callback, Variant<EventListenerOptions, bool> const& options);
+    void add_event_listener(DeprecatedFlyString const& type, IDLEventListener* callback, Variant<AddEventListenerOptions, bool> const& options);
+    void remove_event_listener(DeprecatedFlyString const& type, IDLEventListener* callback, Variant<EventListenerOptions, bool> const& options);
 
     // NOTE: These are for internal use only. They operate as though addEventListener(type, callback) was called instead of addEventListener(type, callback, options).
-    void add_event_listener_without_options(FlyString const& type, IDLEventListener& callback);
-    void remove_event_listener_without_options(FlyString const& type, IDLEventListener& callback);
+    void add_event_listener_without_options(DeprecatedFlyString const& type, IDLEventListener& callback);
+    void remove_event_listener_without_options(DeprecatedFlyString const& type, IDLEventListener& callback);
 
     virtual bool dispatch_event(Event&);
     WebIDL::ExceptionOr<bool> dispatch_event_binding(Event&);
@@ -51,15 +51,15 @@ public:
     virtual void legacy_cancelled_activation_behavior() { }
     virtual void legacy_cancelled_activation_behavior_was_not_called() { }
 
-    WebIDL::CallbackType* event_handler_attribute(FlyString const& name);
-    void set_event_handler_attribute(FlyString const& name, WebIDL::CallbackType*);
+    WebIDL::CallbackType* event_handler_attribute(DeprecatedFlyString const& name);
+    void set_event_handler_attribute(DeprecatedFlyString const& name, WebIDL::CallbackType*);
 
-    bool has_event_listener(FlyString const& type) const;
+    bool has_event_listener(DeprecatedFlyString const& type) const;
 
 protected:
     explicit EventTarget(JS::Realm&);
 
-    void element_event_handler_attribute_changed(FlyString const& local_name, DeprecatedString const& value);
+    void element_event_handler_attribute_changed(DeprecatedFlyString const& local_name, DeprecatedString const& value);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
@@ -68,14 +68,14 @@ private:
 
     // https://html.spec.whatwg.org/multipage/webappapis.html#event-handler-map
     // Spec Note: The order of the entries of event handler map could be arbitrary. It is not observable through any algorithms that operate on the map.
-    HashMap<FlyString, JS::GCPtr<HTML::EventHandler>> m_event_handler_map;
+    HashMap<DeprecatedFlyString, JS::GCPtr<HTML::EventHandler>> m_event_handler_map;
 
-    WebIDL::CallbackType* get_current_value_of_event_handler(FlyString const& name);
-    void activate_event_handler(FlyString const& name, HTML::EventHandler& event_handler);
-    void deactivate_event_handler(FlyString const& name);
-    JS::ThrowCompletionOr<void> process_event_handler_for_event(FlyString const& name, Event& event);
+    WebIDL::CallbackType* get_current_value_of_event_handler(DeprecatedFlyString const& name);
+    void activate_event_handler(DeprecatedFlyString const& name, HTML::EventHandler& event_handler);
+    void deactivate_event_handler(DeprecatedFlyString const& name);
+    JS::ThrowCompletionOr<void> process_event_handler_for_event(DeprecatedFlyString const& name, Event& event);
 };
 
-bool is_window_reflecting_body_element_event_handler(FlyString const& name);
+bool is_window_reflecting_body_element_event_handler(DeprecatedFlyString const& name);
 
 }
diff --git a/Userland/Libraries/LibWeb/DOM/HTMLCollection.cpp b/Userland/Libraries/LibWeb/DOM/HTMLCollection.cpp
index 59b05d09cea..0a9e03b1cc6 100644
--- a/Userland/Libraries/LibWeb/DOM/HTMLCollection.cpp
+++ b/Userland/Libraries/LibWeb/DOM/HTMLCollection.cpp
@@ -62,7 +62,7 @@ Element* HTMLCollection::item(size_t index) const
 }
 
 // https://dom.spec.whatwg.org/#dom-htmlcollection-nameditem-key
-Element* HTMLCollection::named_item(FlyString const& name) const
+Element* HTMLCollection::named_item(DeprecatedFlyString const& name) const
 {
     // 1. If key is the empty string, return null.
     if (name.is_empty())
@@ -130,7 +130,7 @@ JS::Value HTMLCollection::item_value(size_t index) const
     return const_cast<Element*>(element);
 }
 
-JS::Value HTMLCollection::named_item_value(FlyString const& index) const
+JS::Value HTMLCollection::named_item_value(DeprecatedFlyString const& index) const
 {
     auto* element = named_item(index);
     if (!element)
diff --git a/Userland/Libraries/LibWeb/DOM/HTMLCollection.h b/Userland/Libraries/LibWeb/DOM/HTMLCollection.h
index fe48b3a0b49..a221e6b34a7 100644
--- a/Userland/Libraries/LibWeb/DOM/HTMLCollection.h
+++ b/Userland/Libraries/LibWeb/DOM/HTMLCollection.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Function.h>
 #include <LibJS/Heap/GCPtr.h>
 #include <LibWeb/Bindings/LegacyPlatformObject.h>
@@ -35,12 +35,12 @@ public:
 
     size_t length();
     Element* item(size_t index) const;
-    Element* named_item(FlyString const& name) const;
+    Element* named_item(DeprecatedFlyString const& name) const;
 
     JS::MarkedVector<Element*> collect_matching_elements() const;
 
     virtual JS::Value item_value(size_t index) const override;
-    virtual JS::Value named_item_value(FlyString const& name) const override;
+    virtual JS::Value named_item_value(DeprecatedFlyString const& name) const override;
     virtual Vector<DeprecatedString> supported_property_names() const override;
     virtual bool is_supported_property_index(u32) const override;
 
diff --git a/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp b/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
index 7c280a9437a..9f29f539d68 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
+++ b/Userland/Libraries/LibWeb/DOM/MutationRecord.cpp
@@ -12,12 +12,12 @@
 
 namespace Web::DOM {
 
-JS::NonnullGCPtr<MutationRecord> MutationRecord::create(JS::Realm& realm, FlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
+JS::NonnullGCPtr<MutationRecord> MutationRecord::create(JS::Realm& realm, DeprecatedFlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
 {
     return realm.heap().allocate<MutationRecord>(realm, realm, type, target, added_nodes, removed_nodes, previous_sibling, next_sibling, attribute_name, attribute_namespace, old_value);
 }
 
-MutationRecord::MutationRecord(JS::Realm& realm, FlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
+MutationRecord::MutationRecord(JS::Realm& realm, DeprecatedFlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value)
     : PlatformObject(realm)
     , m_type(type)
     , m_target(JS::make_handle(target))
diff --git a/Userland/Libraries/LibWeb/DOM/MutationRecord.h b/Userland/Libraries/LibWeb/DOM/MutationRecord.h
index 6c44f0e06af..5c5f296c013 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationRecord.h
+++ b/Userland/Libraries/LibWeb/DOM/MutationRecord.h
@@ -15,11 +15,11 @@ class MutationRecord : public Bindings::PlatformObject {
     WEB_PLATFORM_OBJECT(MutationRecord, Bindings::PlatformObject);
 
 public:
-    static JS::NonnullGCPtr<MutationRecord> create(JS::Realm&, FlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
+    static JS::NonnullGCPtr<MutationRecord> create(JS::Realm&, DeprecatedFlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
 
     virtual ~MutationRecord() override;
 
-    FlyString const& type() const { return m_type; }
+    DeprecatedFlyString const& type() const { return m_type; }
     Node const* target() const { return m_target; }
     NodeList const* added_nodes() const { return m_added_nodes; }
     NodeList const* removed_nodes() const { return m_removed_nodes; }
@@ -30,10 +30,10 @@ public:
     DeprecatedString const& old_value() const { return m_old_value; }
 
 private:
-    MutationRecord(JS::Realm& realm, FlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
+    MutationRecord(JS::Realm& realm, DeprecatedFlyString const& type, Node& target, NodeList& added_nodes, NodeList& removed_nodes, Node* previous_sibling, Node* next_sibling, DeprecatedString const& attribute_name, DeprecatedString const& attribute_namespace, DeprecatedString const& old_value);
     virtual void visit_edges(Cell::Visitor&) override;
 
-    FlyString m_type;
+    DeprecatedFlyString m_type;
     JS::GCPtr<Node> m_target;
     JS::GCPtr<NodeList> m_added_nodes;
     JS::GCPtr<NodeList> m_removed_nodes;
diff --git a/Userland/Libraries/LibWeb/DOM/MutationType.cpp b/Userland/Libraries/LibWeb/DOM/MutationType.cpp
index 32787e8426b..976c70a0ec4 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationType.cpp
+++ b/Userland/Libraries/LibWeb/DOM/MutationType.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::DOM::MutationType {
 
-#define __ENUMERATE_MUTATION_TYPE(name) FlyString name;
+#define __ENUMERATE_MUTATION_TYPE(name) DeprecatedFlyString name;
 ENUMERATE_MUTATION_TYPES
 #undef __ENUMERATE_MUTATION_TYPE
 
diff --git a/Userland/Libraries/LibWeb/DOM/MutationType.h b/Userland/Libraries/LibWeb/DOM/MutationType.h
index 23f0b8c62a3..e7ddb4c7139 100644
--- a/Userland/Libraries/LibWeb/DOM/MutationType.h
+++ b/Userland/Libraries/LibWeb/DOM/MutationType.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::DOM::MutationType {
 
@@ -15,7 +15,7 @@ namespace Web::DOM::MutationType {
     __ENUMERATE_MUTATION_TYPE(characterData) \
     __ENUMERATE_MUTATION_TYPE(childList)
 
-#define __ENUMERATE_MUTATION_TYPE(name) extern FlyString name;
+#define __ENUMERATE_MUTATION_TYPE(name) extern DeprecatedFlyString name;
 ENUMERATE_MUTATION_TYPES
 #undef __ENUMERATE_MUTATION_TYPE
 
diff --git a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
index 8d2102de5a2..634613a2d5e 100644
--- a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
+++ b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.cpp
@@ -301,7 +301,7 @@ JS::Value NamedNodeMap::item_value(size_t index) const
     return node;
 }
 
-JS::Value NamedNodeMap::named_item_value(FlyString const& name) const
+JS::Value NamedNodeMap::named_item_value(DeprecatedFlyString const& name) const
 {
     auto const* node = get_named_item(name);
     if (!node)
diff --git a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
index e8ccfad02e3..2cb81271b18 100644
--- a/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
+++ b/Userland/Libraries/LibWeb/DOM/NamedNodeMap.h
@@ -28,7 +28,7 @@ public:
     virtual bool is_supported_property_index(u32 index) const override;
     virtual Vector<DeprecatedString> supported_property_names() const override;
     virtual JS::Value item_value(size_t index) const override;
-    virtual JS::Value named_item_value(FlyString const& name) const override;
+    virtual JS::Value named_item_value(DeprecatedFlyString const& name) const override;
 
     size_t length() const { return m_attributes.size(); }
     bool is_empty() const { return m_attributes.is_empty(); }
diff --git a/Userland/Libraries/LibWeb/DOM/Node.cpp b/Userland/Libraries/LibWeb/DOM/Node.cpp
index 29296824656..5da4574a659 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Node.cpp
@@ -126,7 +126,7 @@ const HTML::HTMLElement* Node::enclosing_html_element() const
     return first_ancestor_of_type<HTML::HTMLElement>();
 }
 
-const HTML::HTMLElement* Node::enclosing_html_element_with_attribute(FlyString const& attribute) const
+const HTML::HTMLElement* Node::enclosing_html_element_with_attribute(DeprecatedFlyString const& attribute) const
 {
     for (auto* node = this; node; node = node->parent()) {
         if (is<HTML::HTMLElement>(*node) && verify_cast<HTML::HTMLElement>(*node).has_attribute(attribute))
@@ -1375,7 +1375,7 @@ Painting::PaintableBox const* Node::paint_box() const
 }
 
 // https://dom.spec.whatwg.org/#queue-a-mutation-record
-void Node::queue_mutation_record(FlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling)
+void Node::queue_mutation_record(DeprecatedFlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling)
 {
     // NOTE: We defer garbage collection until the end of the scope, since we can't safely use MutationObserver* as a hashmap key otherwise.
     // FIXME: This is a total hack.
diff --git a/Userland/Libraries/LibWeb/DOM/Node.h b/Userland/Libraries/LibWeb/DOM/Node.h
index 01bfbe6cea3..580f4e347f9 100644
--- a/Userland/Libraries/LibWeb/DOM/Node.h
+++ b/Userland/Libraries/LibWeb/DOM/Node.h
@@ -108,7 +108,7 @@ public:
     JS::NonnullGCPtr<NodeList> child_nodes();
     Vector<JS::Handle<Node>> children_as_vector() const;
 
-    virtual FlyString node_name() const = 0;
+    virtual DeprecatedFlyString node_name() const = 0;
 
     DeprecatedString base_uri() const;
 
@@ -126,7 +126,7 @@ public:
 
     const HTML::HTMLAnchorElement* enclosing_link_element() const;
     const HTML::HTMLElement* enclosing_html_element() const;
-    const HTML::HTMLElement* enclosing_html_element_with_attribute(FlyString const&) const;
+    const HTML::HTMLElement* enclosing_html_element_with_attribute(DeprecatedFlyString const&) const;
 
     DeprecatedString child_text_content() const;
 
@@ -223,7 +223,7 @@ public:
 
     void add_registered_observer(RegisteredObserver& registered_observer) { m_registered_observer_list.append(registered_observer); }
 
-    void queue_mutation_record(FlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling);
+    void queue_mutation_record(DeprecatedFlyString const& type, DeprecatedString attribute_name, DeprecatedString attribute_namespace, DeprecatedString old_value, JS::NonnullGCPtr<NodeList> added_nodes, JS::NonnullGCPtr<NodeList> removed_nodes, Node* previous_sibling, Node* next_sibling);
 
     // https://dom.spec.whatwg.org/#concept-shadow-including-descendant
     template<typename Callback>
diff --git a/Userland/Libraries/LibWeb/DOM/NonElementParentNode.h b/Userland/Libraries/LibWeb/DOM/NonElementParentNode.h
index 8956e023f68..060e1e1eeb7 100644
--- a/Userland/Libraries/LibWeb/DOM/NonElementParentNode.h
+++ b/Userland/Libraries/LibWeb/DOM/NonElementParentNode.h
@@ -17,7 +17,7 @@ namespace Web::DOM {
 template<typename NodeType>
 class NonElementParentNode {
 public:
-    JS::GCPtr<Element> get_element_by_id(FlyString const& id) const
+    JS::GCPtr<Element> get_element_by_id(DeprecatedFlyString const& id) const
     {
         JS::GCPtr<Element> found_element;
         static_cast<NodeType const*>(this)->template for_each_in_inclusive_subtree_of_type<Element>([&](auto& element) {
@@ -29,7 +29,7 @@ public:
         });
         return found_element;
     }
-    JS::GCPtr<Element> get_element_by_id(FlyString const& id)
+    JS::GCPtr<Element> get_element_by_id(DeprecatedFlyString const& id)
     {
         return const_cast<NonElementParentNode const*>(this)->get_element_by_id(id);
     }
diff --git a/Userland/Libraries/LibWeb/DOM/ParentNode.cpp b/Userland/Libraries/LibWeb/DOM/ParentNode.cpp
index c27765d43fe..8654ac65261 100644
--- a/Userland/Libraries/LibWeb/DOM/ParentNode.cpp
+++ b/Userland/Libraries/LibWeb/DOM/ParentNode.cpp
@@ -103,7 +103,7 @@ JS::NonnullGCPtr<HTMLCollection> ParentNode::children()
 
 // https://dom.spec.whatwg.org/#concept-getelementsbytagname
 // NOTE: This method is only exposed on Document and Element, but is in ParentNode to prevent code duplication.
-JS::NonnullGCPtr<HTMLCollection> ParentNode::get_elements_by_tag_name(FlyString const& qualified_name)
+JS::NonnullGCPtr<HTMLCollection> ParentNode::get_elements_by_tag_name(DeprecatedFlyString const& qualified_name)
 {
     // 1. If qualifiedName is "*" (U+002A), return a HTMLCollection rooted at root, whose filter matches only descendant elements.
     if (qualified_name == "*") {
@@ -132,7 +132,7 @@ JS::NonnullGCPtr<HTMLCollection> ParentNode::get_elements_by_tag_name(FlyString
 
 // https://dom.spec.whatwg.org/#concept-getelementsbytagnamens
 // NOTE: This method is only exposed on Document and Element, but is in ParentNode to prevent code duplication.
-JS::NonnullGCPtr<HTMLCollection> ParentNode::get_elements_by_tag_name_ns(FlyString const& nullable_namespace, FlyString const& local_name)
+JS::NonnullGCPtr<HTMLCollection> ParentNode::get_elements_by_tag_name_ns(DeprecatedFlyString const& nullable_namespace, DeprecatedFlyString const& local_name)
 {
     // 1. If namespace is the empty string, set it to null.
     DeprecatedString namespace_ = nullable_namespace;
diff --git a/Userland/Libraries/LibWeb/DOM/ParentNode.h b/Userland/Libraries/LibWeb/DOM/ParentNode.h
index 5dd6acf4d94..4501822bd34 100644
--- a/Userland/Libraries/LibWeb/DOM/ParentNode.h
+++ b/Userland/Libraries/LibWeb/DOM/ParentNode.h
@@ -28,8 +28,8 @@ public:
 
     JS::NonnullGCPtr<HTMLCollection> children();
 
-    JS::NonnullGCPtr<HTMLCollection> get_elements_by_tag_name(FlyString const&);
-    JS::NonnullGCPtr<HTMLCollection> get_elements_by_tag_name_ns(FlyString const&, FlyString const&);
+    JS::NonnullGCPtr<HTMLCollection> get_elements_by_tag_name(DeprecatedFlyString const&);
+    JS::NonnullGCPtr<HTMLCollection> get_elements_by_tag_name_ns(DeprecatedFlyString const&, DeprecatedFlyString const&);
 
     WebIDL::ExceptionOr<void> prepend(Vector<Variant<JS::Handle<Node>, DeprecatedString>> const& nodes);
     WebIDL::ExceptionOr<void> append(Vector<Variant<JS::Handle<Node>, DeprecatedString>> const& nodes);
diff --git a/Userland/Libraries/LibWeb/DOM/ProcessingInstruction.h b/Userland/Libraries/LibWeb/DOM/ProcessingInstruction.h
index 6d6e6ff1600..f4f989b98ba 100644
--- a/Userland/Libraries/LibWeb/DOM/ProcessingInstruction.h
+++ b/Userland/Libraries/LibWeb/DOM/ProcessingInstruction.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibWeb/DOM/CharacterData.h>
 
 namespace Web::DOM {
@@ -17,7 +17,7 @@ class ProcessingInstruction final : public CharacterData {
 public:
     virtual ~ProcessingInstruction() override = default;
 
-    virtual FlyString node_name() const override { return m_target; }
+    virtual DeprecatedFlyString node_name() const override { return m_target; }
 
     DeprecatedString const& target() const { return m_target; }
 
diff --git a/Userland/Libraries/LibWeb/DOM/QualifiedName.cpp b/Userland/Libraries/LibWeb/DOM/QualifiedName.cpp
index f713ab8e193..46ee475ea83 100644
--- a/Userland/Libraries/LibWeb/DOM/QualifiedName.cpp
+++ b/Userland/Libraries/LibWeb/DOM/QualifiedName.cpp
@@ -25,7 +25,7 @@ struct ImplTraits : public Traits<QualifiedName::Impl*> {
 
 static HashTable<QualifiedName::Impl*, ImplTraits> impls;
 
-static NonnullRefPtr<QualifiedName::Impl> ensure_impl(FlyString const& local_name, FlyString const& prefix, FlyString const& namespace_)
+static NonnullRefPtr<QualifiedName::Impl> ensure_impl(DeprecatedFlyString const& local_name, DeprecatedFlyString const& prefix, DeprecatedFlyString const& namespace_)
 {
     auto hash = pair_int_hash(local_name.hash(), pair_int_hash(prefix.hash(), namespace_.hash()));
     auto it = impls.find(hash, [&](QualifiedName::Impl* entry) {
@@ -38,12 +38,12 @@ static NonnullRefPtr<QualifiedName::Impl> ensure_impl(FlyString const& local_nam
     return adopt_ref(*new QualifiedName::Impl(local_name, prefix, namespace_));
 }
 
-QualifiedName::QualifiedName(FlyString const& local_name, FlyString const& prefix, FlyString const& namespace_)
+QualifiedName::QualifiedName(DeprecatedFlyString const& local_name, DeprecatedFlyString const& prefix, DeprecatedFlyString const& namespace_)
     : m_impl(ensure_impl(local_name, prefix, namespace_))
 {
 }
 
-QualifiedName::Impl::Impl(FlyString const& a_local_name, FlyString const& a_prefix, FlyString const& a_namespace)
+QualifiedName::Impl::Impl(DeprecatedFlyString const& a_local_name, DeprecatedFlyString const& a_prefix, DeprecatedFlyString const& a_namespace)
     : local_name(a_local_name)
     , prefix(a_prefix)
     , namespace_(a_namespace)
diff --git a/Userland/Libraries/LibWeb/DOM/QualifiedName.h b/Userland/Libraries/LibWeb/DOM/QualifiedName.h
index 9bc0a0507e4..14d69d60bc9 100644
--- a/Userland/Libraries/LibWeb/DOM/QualifiedName.h
+++ b/Userland/Libraries/LibWeb/DOM/QualifiedName.h
@@ -7,28 +7,28 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::DOM {
 
 class QualifiedName {
 public:
-    QualifiedName(FlyString const& local_name, FlyString const& prefix, FlyString const& namespace_);
+    QualifiedName(DeprecatedFlyString const& local_name, DeprecatedFlyString const& prefix, DeprecatedFlyString const& namespace_);
 
-    FlyString const& local_name() const { return m_impl->local_name; }
-    FlyString const& prefix() const { return m_impl->prefix; }
-    FlyString const& namespace_() const { return m_impl->namespace_; }
+    DeprecatedFlyString const& local_name() const { return m_impl->local_name; }
+    DeprecatedFlyString const& prefix() const { return m_impl->prefix; }
+    DeprecatedFlyString const& namespace_() const { return m_impl->namespace_; }
 
     DeprecatedString const& as_string() const { return m_impl->as_string; }
 
     struct Impl : public RefCounted<Impl> {
-        Impl(FlyString const& local_name, FlyString const& prefix, FlyString const& namespace_);
+        Impl(DeprecatedFlyString const& local_name, DeprecatedFlyString const& prefix, DeprecatedFlyString const& namespace_);
         ~Impl();
 
         void make_internal_string();
-        FlyString local_name;
-        FlyString prefix;
-        FlyString namespace_;
+        DeprecatedFlyString local_name;
+        DeprecatedFlyString prefix;
+        DeprecatedFlyString namespace_;
         DeprecatedString as_string;
     };
 
diff --git a/Userland/Libraries/LibWeb/DOM/ShadowRoot.h b/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
index 843ec98128b..327cf40a89b 100644
--- a/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
+++ b/Userland/Libraries/LibWeb/DOM/ShadowRoot.h
@@ -35,7 +35,7 @@ private:
     ShadowRoot(Document&, Element&);
 
     // ^Node
-    virtual FlyString node_name() const override { return "#shadow-root"; }
+    virtual DeprecatedFlyString node_name() const override { return "#shadow-root"; }
     virtual bool is_shadow_root() const final { return true; }
 
     // NOTE: The specification doesn't seem to specify a default value for closed. Assuming false for now.
diff --git a/Userland/Libraries/LibWeb/DOM/Text.h b/Userland/Libraries/LibWeb/DOM/Text.h
index bca9bca7777..86663192e15 100644
--- a/Userland/Libraries/LibWeb/DOM/Text.h
+++ b/Userland/Libraries/LibWeb/DOM/Text.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <LibWeb/DOM/CharacterData.h>
 
 namespace Web::DOM {
@@ -21,7 +21,7 @@ public:
     static JS::NonnullGCPtr<Text> construct_impl(JS::Realm& realm, DeprecatedString const& data);
 
     // ^Node
-    virtual FlyString node_name() const override { return "#text"; }
+    virtual DeprecatedFlyString node_name() const override { return "#text"; }
     virtual bool is_editable() const override { return m_always_editable || CharacterData::is_editable(); }
 
     void set_always_editable(bool b) { m_always_editable = b; }
diff --git a/Userland/Libraries/LibWeb/DOMParsing/XMLSerializer.cpp b/Userland/Libraries/LibWeb/DOMParsing/XMLSerializer.cpp
index 42f5d23ca05..a06ff25f4ab 100644
--- a/Userland/Libraries/LibWeb/DOMParsing/XMLSerializer.cpp
+++ b/Userland/Libraries/LibWeb/DOMParsing/XMLSerializer.cpp
@@ -41,7 +41,7 @@ WebIDL::ExceptionOr<DeprecatedString> XMLSerializer::serialize_to_string(JS::Non
 }
 
 // https://w3c.github.io/DOM-Parsing/#dfn-add
-static void add_prefix_to_namespace_prefix_map(HashMap<FlyString, Vector<DeprecatedString>>& prefix_map, DeprecatedString const& prefix, FlyString const& namespace_)
+static void add_prefix_to_namespace_prefix_map(HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& prefix_map, DeprecatedString const& prefix, DeprecatedFlyString const& namespace_)
 {
     // 1. Let candidates list be the result of retrieving a list from map where there exists a key in map that matches the value of ns or if there is no such key, then let candidates list be null.
     auto candidates_list_iterator = prefix_map.find(namespace_);
@@ -59,7 +59,7 @@ static void add_prefix_to_namespace_prefix_map(HashMap<FlyString, Vector<Depreca
 }
 
 // https://w3c.github.io/DOM-Parsing/#dfn-retrieving-a-preferred-prefix-string
-static Optional<DeprecatedString> retrieve_a_preferred_prefix_string(DeprecatedString const& preferred_prefix, HashMap<FlyString, Vector<DeprecatedString>> const& namespace_prefix_map, FlyString const& namespace_)
+static Optional<DeprecatedString> retrieve_a_preferred_prefix_string(DeprecatedString const& preferred_prefix, HashMap<DeprecatedFlyString, Vector<DeprecatedString>> const& namespace_prefix_map, DeprecatedFlyString const& namespace_)
 {
     // 1. Let candidates list be the result of retrieving a list from map where there exists a key in map that matches the value of ns or if there is no such key,
     //    then stop running these steps, and return the null value.
@@ -85,7 +85,7 @@ static Optional<DeprecatedString> retrieve_a_preferred_prefix_string(DeprecatedS
 }
 
 // https://w3c.github.io/DOM-Parsing/#dfn-generating-a-prefix
-static DeprecatedString generate_a_prefix(HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, FlyString const& new_namespace, u64& prefix_index)
+static DeprecatedString generate_a_prefix(HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, DeprecatedFlyString const& new_namespace, u64& prefix_index)
 {
     // 1. Let generated prefix be the concatenation of the string "ns" and the current numerical value of prefix index.
     auto generated_prefix = DeprecatedString::formatted("ns{}", prefix_index);
@@ -101,7 +101,7 @@ static DeprecatedString generate_a_prefix(HashMap<FlyString, Vector<DeprecatedSt
 }
 
 // https://w3c.github.io/DOM-Parsing/#dfn-found
-static bool prefix_is_in_prefix_map(DeprecatedString const& prefix, HashMap<FlyString, Vector<DeprecatedString>> const& namespace_prefix_map, FlyString const& namespace_)
+static bool prefix_is_in_prefix_map(DeprecatedString const& prefix, HashMap<DeprecatedFlyString, Vector<DeprecatedString>> const& namespace_prefix_map, DeprecatedFlyString const& namespace_)
 {
     // 1. Let candidates list be the result of retrieving a list from map where there exists a key in map that matches the value of ns
     //    or if there is no such key, then stop running these steps, and return false.
@@ -113,7 +113,7 @@ static bool prefix_is_in_prefix_map(DeprecatedString const& prefix, HashMap<FlyS
     return candidates_list_iterator->value.contains_slow(prefix);
 }
 
-WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string_impl(JS::NonnullGCPtr<DOM::Node> root, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
+WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string_impl(JS::NonnullGCPtr<DOM::Node> root, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
 
 // https://w3c.github.io/DOM-Parsing/#dfn-xml-serialization
 WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string(JS::NonnullGCPtr<DOM::Node> root, RequireWellFormed require_well_formed)
@@ -121,10 +121,10 @@ WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string(JS::NonnullGC
     // 1. Let namespace be a context namespace with value null. The context namespace tracks the XML serialization algorithm's current default namespace.
     //    The context namespace is changed when either an Element Node has a default namespace declaration, or the algorithm generates a default namespace declaration
     //    for the Element Node to match its own namespace. The algorithm assumes no namespace (null) to start.
-    Optional<FlyString> namespace_;
+    Optional<DeprecatedFlyString> namespace_;
 
     // 2. Let prefix map be a new namespace prefix map.
-    HashMap<FlyString, Vector<DeprecatedString>> prefix_map;
+    HashMap<DeprecatedFlyString, Vector<DeprecatedString>> prefix_map;
 
     // 3. Add the XML namespace with prefix value "xml" to prefix map.
     add_prefix_to_namespace_prefix_map(prefix_map, "xml"sv, Namespace::XML);
@@ -140,16 +140,16 @@ WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string(JS::NonnullGC
     return serialize_node_to_xml_string_impl(root, namespace_, prefix_map, prefix_index, require_well_formed);
 }
 
-static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element const& element, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
-static WebIDL::ExceptionOr<DeprecatedString> serialize_document(DOM::Document const& document, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
+static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element const& element, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
+static WebIDL::ExceptionOr<DeprecatedString> serialize_document(DOM::Document const& document, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
 static WebIDL::ExceptionOr<DeprecatedString> serialize_comment(DOM::Comment const& comment, RequireWellFormed require_well_formed);
 static WebIDL::ExceptionOr<DeprecatedString> serialize_text(DOM::Text const& text, RequireWellFormed require_well_formed);
-static WebIDL::ExceptionOr<DeprecatedString> serialize_document_fragment(DOM::DocumentFragment const& document_fragment, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
+static WebIDL::ExceptionOr<DeprecatedString> serialize_document_fragment(DOM::DocumentFragment const& document_fragment, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed);
 static WebIDL::ExceptionOr<DeprecatedString> serialize_document_type(DOM::DocumentType const& document_type, RequireWellFormed require_well_formed);
 static WebIDL::ExceptionOr<DeprecatedString> serialize_processing_instruction(DOM::ProcessingInstruction const& processing_instruction, RequireWellFormed require_well_formed);
 
 // https://w3c.github.io/DOM-Parsing/#dfn-xml-serialization-algorithm
-WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string_impl(JS::NonnullGCPtr<DOM::Node> root, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
+WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string_impl(JS::NonnullGCPtr<DOM::Node> root, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
 {
     // Each of the following algorithms for producing an XML serialization of a DOM node take as input a node to serialize and the following arguments:
     // - A context namespace namespace
@@ -216,7 +216,7 @@ WebIDL::ExceptionOr<DeprecatedString> serialize_node_to_xml_string_impl(JS::Nonn
 }
 
 // https://w3c.github.io/DOM-Parsing/#dfn-recording-the-namespace-information
-static Optional<DeprecatedString> record_namespace_information(DOM::Element const& element, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, HashMap<DeprecatedString, DeprecatedString>& local_prefix_map)
+static Optional<DeprecatedString> record_namespace_information(DOM::Element const& element, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, HashMap<DeprecatedString, DeprecatedString>& local_prefix_map)
 {
     // 1. Let default namespace attr value be null.
     Optional<DeprecatedString> default_namespace_attribute_value;
@@ -306,7 +306,7 @@ struct LocalNameSetEntry {
 };
 
 // https://w3c.github.io/DOM-Parsing/#dfn-xml-serialization-of-the-attributes
-static WebIDL::ExceptionOr<DeprecatedString> serialize_element_attributes(DOM::Element const& element, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, HashMap<DeprecatedString, DeprecatedString> const& local_prefixes_map, bool ignore_namespace_definition_attribute, RequireWellFormed require_well_formed)
+static WebIDL::ExceptionOr<DeprecatedString> serialize_element_attributes(DOM::Element const& element, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, HashMap<DeprecatedString, DeprecatedString> const& local_prefixes_map, bool ignore_namespace_definition_attribute, RequireWellFormed require_well_formed)
 {
     auto& realm = element.realm();
 
@@ -459,7 +459,7 @@ static WebIDL::ExceptionOr<DeprecatedString> serialize_element_attributes(DOM::E
 }
 
 // https://w3c.github.io/DOM-Parsing/#xml-serializing-an-element-node
-static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element const& element, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
+static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element const& element, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
 {
     auto& realm = element.realm();
 
@@ -486,7 +486,7 @@ static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element cons
     bool ignore_namespace_definition_attribute = false;
 
     // 6. Given prefix map, copy a namespace prefix map and let map be the result.
-    HashMap<FlyString, Vector<DeprecatedString>> map;
+    HashMap<DeprecatedFlyString, Vector<DeprecatedString>> map;
 
     // https://w3c.github.io/DOM-Parsing/#dfn-copy-a-namespace-prefix-map
     // NOTE: This is only used here.
@@ -701,7 +701,7 @@ static WebIDL::ExceptionOr<DeprecatedString> serialize_element(DOM::Element cons
 }
 
 // https://w3c.github.io/DOM-Parsing/#xml-serializing-a-document-node
-static WebIDL::ExceptionOr<DeprecatedString> serialize_document(DOM::Document const& document, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
+static WebIDL::ExceptionOr<DeprecatedString> serialize_document(DOM::Document const& document, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
 {
     // If the require well-formed flag is set (its value is true), and this node has no documentElement (the documentElement attribute's value is null),
     // then throw an exception; the serialization of this node would not be a well-formed document.
@@ -763,7 +763,7 @@ static WebIDL::ExceptionOr<DeprecatedString> serialize_text(DOM::Text const& tex
 }
 
 // https://w3c.github.io/DOM-Parsing/#xml-serializing-a-documentfragment-node
-static WebIDL::ExceptionOr<DeprecatedString> serialize_document_fragment(DOM::DocumentFragment const& document_fragment, Optional<FlyString>& namespace_, HashMap<FlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
+static WebIDL::ExceptionOr<DeprecatedString> serialize_document_fragment(DOM::DocumentFragment const& document_fragment, Optional<DeprecatedFlyString>& namespace_, HashMap<DeprecatedFlyString, Vector<DeprecatedString>>& namespace_prefix_map, u64& prefix_index, RequireWellFormed require_well_formed)
 {
     // 1. Let markup the empty string.
     StringBuilder markup;
diff --git a/Userland/Libraries/LibWeb/Dump.cpp b/Userland/Libraries/LibWeb/Dump.cpp
index 64d1596cc14..fc163df6670 100644
--- a/Userland/Libraries/LibWeb/Dump.cpp
+++ b/Userland/Libraries/LibWeb/Dump.cpp
@@ -92,7 +92,7 @@ void dump_tree(StringBuilder& builder, Layout::Node const& layout_node, bool sho
     for (size_t i = 0; i < indent; ++i)
         builder.append("  "sv);
 
-    FlyString tag_name;
+    DeprecatedFlyString tag_name;
     if (layout_node.is_anonymous())
         tag_name = "(anonymous)";
     else if (is<DOM::Element>(layout_node.dom_node()))
diff --git a/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp b/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
index bbcb29d4620..1979ef261c2 100644
--- a/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
+++ b/Userland/Libraries/LibWeb/Encoding/TextDecoder.cpp
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Runtime/TypedArray.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/Encoding/TextDecoder.h>
@@ -12,7 +12,7 @@
 
 namespace Web::Encoding {
 
-WebIDL::ExceptionOr<JS::NonnullGCPtr<TextDecoder>> TextDecoder::construct_impl(JS::Realm& realm, FlyString encoding)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<TextDecoder>> TextDecoder::construct_impl(JS::Realm& realm, DeprecatedFlyString encoding)
 {
     auto decoder = TextCodec::decoder_for(encoding);
     if (!decoder)
@@ -22,7 +22,7 @@ WebIDL::ExceptionOr<JS::NonnullGCPtr<TextDecoder>> TextDecoder::construct_impl(J
 }
 
 // https://encoding.spec.whatwg.org/#dom-textdecoder
-TextDecoder::TextDecoder(JS::Realm& realm, TextCodec::Decoder& decoder, FlyString encoding, bool fatal, bool ignore_bom)
+TextDecoder::TextDecoder(JS::Realm& realm, TextCodec::Decoder& decoder, DeprecatedFlyString encoding, bool fatal, bool ignore_bom)
     : PlatformObject(realm)
     , m_decoder(decoder)
     , m_encoding(move(encoding))
diff --git a/Userland/Libraries/LibWeb/Encoding/TextDecoder.h b/Userland/Libraries/LibWeb/Encoding/TextDecoder.h
index f2f2a753398..450ca2dbb5d 100644
--- a/Userland/Libraries/LibWeb/Encoding/TextDecoder.h
+++ b/Userland/Libraries/LibWeb/Encoding/TextDecoder.h
@@ -21,22 +21,22 @@ class TextDecoder : public Bindings::PlatformObject {
     WEB_PLATFORM_OBJECT(TextDecoder, Bindings::PlatformObject);
 
 public:
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<TextDecoder>> construct_impl(JS::Realm&, FlyString encoding);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<TextDecoder>> construct_impl(JS::Realm&, DeprecatedFlyString encoding);
 
     virtual ~TextDecoder() override;
 
     WebIDL::ExceptionOr<DeprecatedString> decode(JS::Handle<JS::Object> const&) const;
 
-    FlyString const& encoding() const { return m_encoding; }
+    DeprecatedFlyString const& encoding() const { return m_encoding; }
     bool fatal() const { return m_fatal; }
     bool ignore_bom() const { return m_ignore_bom; };
 
 private:
     // https://encoding.spec.whatwg.org/#dom-textdecoder
-    TextDecoder(JS::Realm&, TextCodec::Decoder&, FlyString encoding, bool fatal, bool ignore_bom);
+    TextDecoder(JS::Realm&, TextCodec::Decoder&, DeprecatedFlyString encoding, bool fatal, bool ignore_bom);
 
     TextCodec::Decoder& m_decoder;
-    FlyString m_encoding;
+    DeprecatedFlyString m_encoding;
     bool m_fatal { false };
     bool m_ignore_bom { false };
 };
diff --git a/Userland/Libraries/LibWeb/Encoding/TextEncoder.cpp b/Userland/Libraries/LibWeb/Encoding/TextEncoder.cpp
index f5128b6520f..c1a44767dc0 100644
--- a/Userland/Libraries/LibWeb/Encoding/TextEncoder.cpp
+++ b/Userland/Libraries/LibWeb/Encoding/TextEncoder.cpp
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 #include <LibJS/Runtime/TypedArray.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/Encoding/TextEncoder.h>
@@ -44,9 +44,9 @@ JS::Uint8Array* TextEncoder::encode(DeprecatedString const& input) const
 }
 
 // https://encoding.spec.whatwg.org/#dom-textencoder-encoding
-FlyString const& TextEncoder::encoding()
+DeprecatedFlyString const& TextEncoder::encoding()
 {
-    static FlyString encoding = "utf-8"sv;
+    static DeprecatedFlyString encoding = "utf-8"sv;
     return encoding;
 }
 
diff --git a/Userland/Libraries/LibWeb/Encoding/TextEncoder.h b/Userland/Libraries/LibWeb/Encoding/TextEncoder.h
index 8161d2f9dea..02eb55d736b 100644
--- a/Userland/Libraries/LibWeb/Encoding/TextEncoder.h
+++ b/Userland/Libraries/LibWeb/Encoding/TextEncoder.h
@@ -26,7 +26,7 @@ public:
 
     JS::Uint8Array* encode(DeprecatedString const& input) const;
 
-    static FlyString const& encoding();
+    static DeprecatedFlyString const& encoding();
 
 protected:
     // https://encoding.spec.whatwg.org/#dom-textencoder
diff --git a/Userland/Libraries/LibWeb/FontCache.h b/Userland/Libraries/LibWeb/FontCache.h
index 56d5e1b8b63..da6d7d996df 100644
--- a/Userland/Libraries/LibWeb/FontCache.h
+++ b/Userland/Libraries/LibWeb/FontCache.h
@@ -6,14 +6,14 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/HashMap.h>
 #include <LibGfx/Font/Font.h>
 #include <LibGfx/Forward.h>
 
 struct FontSelector {
-    FlyString family;
+    DeprecatedFlyString family;
     float point_size { 0 };
     int weight { 0 };
     int slope { 0 };
diff --git a/Userland/Libraries/LibWeb/HTML/AttributeNames.cpp b/Userland/Libraries/LibWeb/HTML/AttributeNames.cpp
index 9bc32452bf8..3d4d0b88fa4 100644
--- a/Userland/Libraries/LibWeb/HTML/AttributeNames.cpp
+++ b/Userland/Libraries/LibWeb/HTML/AttributeNames.cpp
@@ -10,7 +10,7 @@ namespace Web {
 namespace HTML {
 namespace AttributeNames {
 
-#define __ENUMERATE_HTML_ATTRIBUTE(name) FlyString name;
+#define __ENUMERATE_HTML_ATTRIBUTE(name) DeprecatedFlyString name;
 ENUMERATE_HTML_ATTRIBUTES
 #undef __ENUMERATE_HTML_ATTRIBUTE
 
@@ -41,7 +41,7 @@ ENUMERATE_HTML_ATTRIBUTES
 }
 
 // https://html.spec.whatwg.org/#boolean-attribute
-bool is_boolean_attribute(FlyString const& attribute)
+bool is_boolean_attribute(DeprecatedFlyString const& attribute)
 {
     // NOTE: This is the list of attributes from https://html.spec.whatwg.org/#attributes-3
     //       with a Value column value of "Boolean attribute".
diff --git a/Userland/Libraries/LibWeb/HTML/AttributeNames.h b/Userland/Libraries/LibWeb/HTML/AttributeNames.h
index 88d83e94d81..399a820812d 100644
--- a/Userland/Libraries/LibWeb/HTML/AttributeNames.h
+++ b/Userland/Libraries/LibWeb/HTML/AttributeNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web {
 namespace HTML {
@@ -229,13 +229,13 @@ namespace AttributeNames {
     __ENUMERATE_HTML_ATTRIBUTE(width)                      \
     __ENUMERATE_HTML_ATTRIBUTE(wrap)
 
-#define __ENUMERATE_HTML_ATTRIBUTE(name) extern FlyString name;
+#define __ENUMERATE_HTML_ATTRIBUTE(name) extern DeprecatedFlyString name;
 ENUMERATE_HTML_ATTRIBUTES
 #undef __ENUMERATE_HTML_ATTRIBUTE
 
 }
 
-bool is_boolean_attribute(FlyString const& attribute);
+bool is_boolean_attribute(DeprecatedFlyString const& attribute);
 
 }
 }
diff --git a/Userland/Libraries/LibWeb/HTML/CloseEvent.cpp b/Userland/Libraries/LibWeb/HTML/CloseEvent.cpp
index 80b5ea3d07f..1dbd77d1d1f 100644
--- a/Userland/Libraries/LibWeb/HTML/CloseEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/CloseEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-CloseEvent* CloseEvent::create(JS::Realm& realm, FlyString const& event_name, CloseEventInit const& event_init)
+CloseEvent* CloseEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, CloseEventInit const& event_init)
 {
     return realm.heap().allocate<CloseEvent>(realm, realm, event_name, event_init);
 }
 
-CloseEvent* CloseEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, CloseEventInit const& event_init)
+CloseEvent* CloseEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, CloseEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-CloseEvent::CloseEvent(JS::Realm& realm, FlyString const& event_name, CloseEventInit const& event_init)
+CloseEvent::CloseEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, CloseEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_was_clean(event_init.was_clean)
     , m_code(event_init.code)
diff --git a/Userland/Libraries/LibWeb/HTML/CloseEvent.h b/Userland/Libraries/LibWeb/HTML/CloseEvent.h
index 7e92f76f9b1..6c94be526db 100644
--- a/Userland/Libraries/LibWeb/HTML/CloseEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/CloseEvent.h
@@ -21,8 +21,8 @@ class CloseEvent : public DOM::Event {
     WEB_PLATFORM_OBJECT(CloseEvent, DOM::Event);
 
 public:
-    static CloseEvent* create(JS::Realm&, FlyString const& event_name, CloseEventInit const& event_init = {});
-    static CloseEvent* construct_impl(JS::Realm&, FlyString const& event_name, CloseEventInit const& event_init);
+    static CloseEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, CloseEventInit const& event_init = {});
+    static CloseEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, CloseEventInit const& event_init);
 
     virtual ~CloseEvent() override;
 
@@ -31,7 +31,7 @@ public:
     DeprecatedString reason() const { return m_reason; }
 
 private:
-    CloseEvent(JS::Realm&, FlyString const& event_name, CloseEventInit const& event_init);
+    CloseEvent(JS::Realm&, DeprecatedFlyString const& event_name, CloseEventInit const& event_init);
 
     bool m_was_clean { false };
     u16 m_code { 0 };
diff --git a/Userland/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp b/Userland/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
index f1dcf32c692..8ae01fdf5f2 100644
--- a/Userland/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
+++ b/Userland/Libraries/LibWeb/HTML/CrossOrigin/AbstractOperations.cpp
@@ -59,7 +59,7 @@ Vector<CrossOriginProperty> cross_origin_properties(Variant<Bindings::LocationOb
 bool is_cross_origin_accessible_window_property_name(JS::PropertyKey const& property_key)
 {
     // A JavaScript property name P is a cross-origin accessible window property name if it is "window", "self", "location", "close", "closed", "focus", "blur", "frames", "length", "top", "opener", "parent", "postMessage", or an array index property name.
-    static Array<FlyString, 13> property_names {
+    static Array<DeprecatedFlyString, 13> property_names {
         "window"sv, "self"sv, "location"sv, "close"sv, "closed"sv, "focus"sv, "blur"sv, "frames"sv, "length"sv, "top"sv, "opener"sv, "parent"sv, "postMessage"sv
     };
     return (property_key.is_string() && any_of(property_names, [&](auto const& name) { return property_key.as_string() == name; })) || property_key.is_number();
diff --git a/Userland/Libraries/LibWeb/HTML/DOMStringMap.cpp b/Userland/Libraries/LibWeb/HTML/DOMStringMap.cpp
index 2df3643a1a5..a9b2f6b5036 100644
--- a/Userland/Libraries/LibWeb/HTML/DOMStringMap.cpp
+++ b/Userland/Libraries/LibWeb/HTML/DOMStringMap.cpp
@@ -183,7 +183,7 @@ bool DOMStringMap::delete_existing_named_property(DeprecatedString const& name)
     return true;
 }
 
-JS::Value DOMStringMap::named_item_value(FlyString const& name) const
+JS::Value DOMStringMap::named_item_value(DeprecatedFlyString const& name) const
 {
     return JS::PrimitiveString::create(vm(), determine_value_of_named_property(name));
 }
diff --git a/Userland/Libraries/LibWeb/HTML/DOMStringMap.h b/Userland/Libraries/LibWeb/HTML/DOMStringMap.h
index 79dadd85c35..c8d12cab720 100644
--- a/Userland/Libraries/LibWeb/HTML/DOMStringMap.h
+++ b/Userland/Libraries/LibWeb/HTML/DOMStringMap.h
@@ -34,7 +34,7 @@ private:
     virtual void visit_edges(Cell::Visitor&) override;
 
     // ^LegacyPlatformObject
-    virtual JS::Value named_item_value(FlyString const&) const override;
+    virtual JS::Value named_item_value(DeprecatedFlyString const&) const override;
     virtual Vector<DeprecatedString> supported_property_names() const override;
 
     struct NameValuePair {
diff --git a/Userland/Libraries/LibWeb/HTML/ErrorEvent.cpp b/Userland/Libraries/LibWeb/HTML/ErrorEvent.cpp
index 55b0620ba26..e557705fc7b 100644
--- a/Userland/Libraries/LibWeb/HTML/ErrorEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/ErrorEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-ErrorEvent* ErrorEvent::create(JS::Realm& realm, FlyString const& event_name, ErrorEventInit const& event_init)
+ErrorEvent* ErrorEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init)
 {
     return realm.heap().allocate<ErrorEvent>(realm, realm, event_name, event_init);
 }
 
-ErrorEvent* ErrorEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, ErrorEventInit const& event_init)
+ErrorEvent* ErrorEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-ErrorEvent::ErrorEvent(JS::Realm& realm, FlyString const& event_name, ErrorEventInit const& event_init)
+ErrorEvent::ErrorEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init)
     : DOM::Event(realm, event_name)
     , m_message(event_init.message)
     , m_filename(event_init.filename)
diff --git a/Userland/Libraries/LibWeb/HTML/ErrorEvent.h b/Userland/Libraries/LibWeb/HTML/ErrorEvent.h
index 6a8574ffdf8..e4ce4ba2fdb 100644
--- a/Userland/Libraries/LibWeb/HTML/ErrorEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/ErrorEvent.h
@@ -24,8 +24,8 @@ class ErrorEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(ErrorEvent, DOM::Event);
 
 public:
-    static ErrorEvent* create(JS::Realm&, FlyString const& event_name, ErrorEventInit const& event_init = {});
-    static ErrorEvent* construct_impl(JS::Realm&, FlyString const& event_name, ErrorEventInit const& event_init);
+    static ErrorEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init = {});
+    static ErrorEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init);
 
     virtual ~ErrorEvent() override;
 
@@ -45,7 +45,7 @@ public:
     JS::Value error() const { return m_error; }
 
 private:
-    ErrorEvent(JS::Realm&, FlyString const& event_name, ErrorEventInit const& event_init);
+    ErrorEvent(JS::Realm&, DeprecatedFlyString const& event_name, ErrorEventInit const& event_init);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
diff --git a/Userland/Libraries/LibWeb/HTML/EventNames.cpp b/Userland/Libraries/LibWeb/HTML/EventNames.cpp
index 43f611a08bb..f0c0d2e58d1 100644
--- a/Userland/Libraries/LibWeb/HTML/EventNames.cpp
+++ b/Userland/Libraries/LibWeb/HTML/EventNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::HTML::EventNames {
 
-#define __ENUMERATE_HTML_EVENT(name) FlyString name;
+#define __ENUMERATE_HTML_EVENT(name) DeprecatedFlyString name;
 ENUMERATE_HTML_EVENTS
 #undef __ENUMERATE_HTML_EVENT
 
diff --git a/Userland/Libraries/LibWeb/HTML/EventNames.h b/Userland/Libraries/LibWeb/HTML/EventNames.h
index 05fb2bf4d54..911f2bd5cf0 100644
--- a/Userland/Libraries/LibWeb/HTML/EventNames.h
+++ b/Userland/Libraries/LibWeb/HTML/EventNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::HTML::EventNames {
 
@@ -60,7 +60,7 @@ namespace Web::HTML::EventNames {
     __ENUMERATE_HTML_EVENT(unload)                  \
     __ENUMERATE_HTML_EVENT(visibilitychange)
 
-#define __ENUMERATE_HTML_EVENT(name) extern FlyString name;
+#define __ENUMERATE_HTML_EVENT(name) extern DeprecatedFlyString name;
 ENUMERATE_HTML_EVENTS
 #undef __ENUMERATE_HTML_EVENT
 
diff --git a/Userland/Libraries/LibWeb/HTML/GlobalEventHandlers.h b/Userland/Libraries/LibWeb/HTML/GlobalEventHandlers.h
index 23c1908be21..0d6b18a44b8 100644
--- a/Userland/Libraries/LibWeb/HTML/GlobalEventHandlers.h
+++ b/Userland/Libraries/LibWeb/HTML/GlobalEventHandlers.h
@@ -91,7 +91,7 @@ public:
 #undef __ENUMERATE
 
 protected:
-    virtual DOM::EventTarget& global_event_handlers_to_event_target(FlyString const& event_name) = 0;
+    virtual DOM::EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const& event_name) = 0;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.cpp
index 073c160df17..6482ff09c07 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.cpp
@@ -22,7 +22,7 @@ HTMLAnchorElement::HTMLAnchorElement(DOM::Document& document, DOM::QualifiedName
 
 HTMLAnchorElement::~HTMLAnchorElement() = default;
 
-void HTMLAnchorElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLAnchorElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
     if (name == HTML::AttributeNames::href) {
@@ -85,7 +85,7 @@ i32 HTMLAnchorElement::default_tab_index_value() const
     return 0;
 }
 
-FlyString HTMLAnchorElement::default_role() const
+DeprecatedFlyString HTMLAnchorElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-a-no-href
     if (!href().is_null())
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.h b/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.h
index 3356a214004..88cba8c5540 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLAnchorElement.h
@@ -35,7 +35,7 @@ private:
     void run_activation_behavior(Web::DOM::Event const&);
 
     // ^DOM::Element
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
     virtual i32 default_tab_index_value() const override;
 
     // ^HTML::HTMLHyperlinkElementUtils
@@ -51,7 +51,7 @@ private:
         queue_an_element_task(source, move(steps));
     }
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.cpp
index 05bf0624665..ab3efa3f347 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.cpp
@@ -18,7 +18,7 @@ HTMLAreaElement::HTMLAreaElement(DOM::Document& document, DOM::QualifiedName qua
 
 HTMLAreaElement::~HTMLAreaElement() = default;
 
-void HTMLAreaElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLAreaElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
     if (name == HTML::AttributeNames::href) {
@@ -43,7 +43,7 @@ i32 HTMLAreaElement::default_tab_index_value() const
     return 0;
 }
 
-FlyString HTMLAreaElement::default_role() const
+DeprecatedFlyString HTMLAreaElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-area-no-href
     if (!href().is_null())
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.h b/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.h
index 80398dd0a65..4140fdea31b 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLAreaElement.h
@@ -24,7 +24,7 @@ private:
     HTMLAreaElement(DOM::Document&, DOM::QualifiedName);
 
     // ^DOM::Element
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
     virtual i32 default_tab_index_value() const override;
 
     // ^HTML::HTMLHyperlinkElementUtils
@@ -40,7 +40,7 @@ private:
         queue_an_element_task(source, move(steps));
     }
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
index 66d41240df1..4bbbf5584c7 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.cpp
@@ -38,7 +38,7 @@ void HTMLBaseElement::removed_from(Node* parent)
     document().update_base_element({});
 }
 
-void HTMLBaseElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLBaseElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.h b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.h
index 9cc5c5fa9a7..3634f847d90 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBaseElement.h
@@ -23,7 +23,7 @@ public:
 
     virtual void inserted() override;
     virtual void removed_from(Node*) override;
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
 private:
     HTMLBaseElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.cpp
index 5a887ca809d..ea1f4015e2d 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.cpp
@@ -38,7 +38,7 @@ void HTMLBodyElement::apply_presentational_hints(CSS::StyleProperties& style) co
     });
 }
 
-void HTMLBodyElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLBodyElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
     if (name.equals_ignoring_case("link"sv)) {
@@ -71,7 +71,7 @@ void HTMLBodyElement::parse_attribute(FlyString const& name, DeprecatedString co
 #undef __ENUMERATE
 }
 
-DOM::EventTarget& HTMLBodyElement::global_event_handlers_to_event_target(FlyString const& event_name)
+DOM::EventTarget& HTMLBodyElement::global_event_handlers_to_event_target(DeprecatedFlyString const& event_name)
 {
     // NOTE: This is a little weird, but IIUC document.body.onload actually refers to window.onload
     // NOTE: document.body can return either a HTMLBodyElement or HTMLFrameSetElement, so both these elements must support this mapping.
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.h b/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.h
index e1ff7613cbc..1fb06052d55 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLBodyElement.h
@@ -20,17 +20,17 @@ class HTMLBodyElement final
 public:
     virtual ~HTMLBodyElement() override;
 
-    virtual void parse_attribute(FlyString const&, DeprecatedString const&) override;
+    virtual void parse_attribute(DeprecatedFlyString const&, DeprecatedString const&) override;
     virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
     // https://www.w3.org/TR/html-aria/#el-body
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::generic; };
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::generic; };
 
 private:
     HTMLBodyElement(DOM::Document&, DOM::QualifiedName);
 
     // ^HTML::GlobalEventHandlers
-    virtual EventTarget& global_event_handlers_to_event_target(FlyString const& event_name) override;
+    virtual EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const& event_name) override;
 
     // ^HTML::WindowEventHandlers
     virtual EventTarget& window_event_handlers_to_event_target() override;
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLButtonElement.h b/Userland/Libraries/LibWeb/HTML/HTMLButtonElement.h
index 64c80335269..82f9646fdd3 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLButtonElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLButtonElement.h
@@ -55,7 +55,7 @@ public:
     virtual bool is_labelable() const override { return true; }
 
     // https://www.w3.org/TR/html-aria/#el-button
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::button; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::button; }
 
 private:
     HTMLButtonElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLDataElement.h b/Userland/Libraries/LibWeb/HTML/HTMLDataElement.h
index c2e0a6ad67c..45b4e0aa34c 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLDataElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLDataElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLDataElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-data
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::generic; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::generic; }
 
 private:
     HTMLDataElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLDataListElement.h b/Userland/Libraries/LibWeb/HTML/HTMLDataListElement.h
index 4de4419fb9e..1decc6f6a0d 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLDataListElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLDataListElement.h
@@ -17,7 +17,7 @@ class HTMLDataListElement final : public HTMLElement {
 public:
     virtual ~HTMLDataListElement() override;
 
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::listbox; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::listbox; }
 
 private:
     HTMLDataListElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLDetailsElement.h b/Userland/Libraries/LibWeb/HTML/HTMLDetailsElement.h
index 26eedd4219f..11082c9ea42 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLDetailsElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLDetailsElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLDetailsElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-details
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::group; };
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::group; };
 
 private:
     HTMLDetailsElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLDialogElement.h b/Userland/Libraries/LibWeb/HTML/HTMLDialogElement.h
index b81e6c1d3cc..4dbb6fc0345 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLDialogElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLDialogElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLDialogElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-dialog
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::dialog; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::dialog; }
 
 private:
     HTMLDialogElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLDivElement.h b/Userland/Libraries/LibWeb/HTML/HTMLDivElement.h
index 0dda8e975f6..064515fa9bc 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLDivElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLDivElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLDivElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-div
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::generic; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::generic; }
 
 private:
     HTMLDivElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLElement.cpp
index 27c5447f87c..35a146ac07a 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLElement.cpp
@@ -232,7 +232,7 @@ bool HTMLElement::cannot_navigate() const
     return !is<HTML::HTMLAnchorElement>(this) && !is_connected();
 }
 
-void HTMLElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     Element::parse_attribute(name, value);
 
@@ -270,7 +270,7 @@ void HTMLElement::focus()
 }
 
 // https://html.spec.whatwg.org/multipage/webappapis.html#fire-a-synthetic-pointer-event
-bool HTMLElement::fire_a_synthetic_pointer_event(FlyString const& type, DOM::Element& target, bool not_trusted)
+bool HTMLElement::fire_a_synthetic_pointer_event(DeprecatedFlyString const& type, DOM::Element& target, bool not_trusted)
 {
     // 1. Let event be the result of creating an event using PointerEvent.
     // 2. Initialize event's type attribute to e.
@@ -328,7 +328,7 @@ void HTMLElement::blur()
     // User agents may selectively or uniformly ignore calls to this method for usability reasons.
 }
 
-FlyString HTMLElement::default_role() const
+DeprecatedFlyString HTMLElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-article
     if (local_name() == TagNames::article)
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLElement.h b/Userland/Libraries/LibWeb/HTML/HTMLElement.h
index 9e1c1a402ec..a31d67f0b41 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLElement.h
@@ -54,19 +54,19 @@ public:
 
     void blur();
 
-    bool fire_a_synthetic_pointer_event(FlyString const& type, DOM::Element& target, bool not_trusted);
+    bool fire_a_synthetic_pointer_event(DeprecatedFlyString const& type, DOM::Element& target, bool not_trusted);
 
     // https://html.spec.whatwg.org/multipage/forms.html#category-label
     virtual bool is_labelable() const { return false; }
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 protected:
     HTMLElement(DOM::Document&, DOM::QualifiedName);
 
     virtual void initialize(JS::Realm&) override;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual void visit_edges(Cell::Visitor&) override;
 
@@ -74,7 +74,7 @@ private:
     virtual bool is_html_element() const final { return true; }
 
     // ^HTML::GlobalEventHandlers
-    virtual DOM::EventTarget& global_event_handlers_to_event_target(FlyString const&) override { return *this; }
+    virtual DOM::EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const&) override { return *this; }
 
     enum class ContentEditableState {
         True,
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.h b/Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.h
index 532b62da3e6..6b2e3ab1fa4 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLFieldSetElement.h
@@ -36,7 +36,7 @@ public:
     // https://html.spec.whatwg.org/multipage/forms.html#category-autocapitalize
     virtual bool is_auto_capitalize_inheriting() const override { return true; }
 
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::group; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::group; }
 
 private:
     HTMLFieldSetElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLFormElement.h b/Userland/Libraries/LibWeb/HTML/HTMLFormElement.h
index e380d68d1df..928c469d3be 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLFormElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLFormElement.h
@@ -38,7 +38,7 @@ public:
     unsigned length() const;
 
     // https://www.w3.org/TR/html-aria/#el-form
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::form; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::form; }
 
 private:
     HTMLFormElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp
index c5359f55866..90af8cf9103 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp
@@ -18,7 +18,7 @@ HTMLFrameSetElement::HTMLFrameSetElement(DOM::Document& document, DOM::Qualified
 
 HTMLFrameSetElement::~HTMLFrameSetElement() = default;
 
-void HTMLFrameSetElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLFrameSetElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
 
@@ -31,7 +31,7 @@ void HTMLFrameSetElement::parse_attribute(FlyString const& name, DeprecatedStrin
 #undef __ENUMERATE
 }
 
-DOM::EventTarget& HTMLFrameSetElement::global_event_handlers_to_event_target(FlyString const& event_name)
+DOM::EventTarget& HTMLFrameSetElement::global_event_handlers_to_event_target(DeprecatedFlyString const& event_name)
 {
     // NOTE: This is a little weird, but IIUC document.body.onload actually refers to window.onload
     // NOTE: document.body can return either a HTMLBodyElement or HTMLFrameSetElement, so both these elements must support this mapping.
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.h b/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.h
index 371e1ca1d2b..0a3ef76f588 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.h
@@ -23,11 +23,11 @@ public:
 private:
     HTMLFrameSetElement(DOM::Document&, DOM::QualifiedName);
 
-    virtual void parse_attribute(FlyString const&, DeprecatedString const&) override;
+    virtual void parse_attribute(DeprecatedFlyString const&, DeprecatedString const&) override;
 
 private:
     // ^HTML::GlobalEventHandlers
-    virtual EventTarget& global_event_handlers_to_event_target(FlyString const& event_name) override;
+    virtual EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const& event_name) override;
 
     // ^HTML::WindowEventHandlers
     virtual EventTarget& window_event_handlers_to_event_target() override;
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLHRElement.h b/Userland/Libraries/LibWeb/HTML/HTMLHRElement.h
index 4b13e4882e6..e1c4e9ef84e 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLHRElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLHRElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLHRElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-hr
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::separator; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::separator; }
 
 private:
     HTMLHRElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLHeadingElement.h b/Userland/Libraries/LibWeb/HTML/HTMLHeadingElement.h
index 6093993ce3a..892c1fcbe0e 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLHeadingElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLHeadingElement.h
@@ -20,7 +20,7 @@ public:
     virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
     // https://www.w3.org/TR/html-aria/#el-h1-h6
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::heading; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::heading; }
     virtual DeprecatedString aria_level() const override
     {
         // TODO: aria-level = the number in the element's tag name
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLHtmlElement.h b/Userland/Libraries/LibWeb/HTML/HTMLHtmlElement.h
index 272d6af62a6..88014cdaeb0 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLHtmlElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLHtmlElement.h
@@ -20,7 +20,7 @@ public:
     bool should_use_body_background_properties() const;
 
     // https://www.w3.org/TR/html-aria/#el-html
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::document; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::document; }
 
 private:
     HTMLHtmlElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.cpp
index 2713f7563fe..92b760a7e24 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.cpp
@@ -27,7 +27,7 @@ JS::GCPtr<Layout::Node> HTMLIFrameElement::create_layout_node(NonnullRefPtr<CSS:
     return heap().allocate_without_realm<Layout::FrameBox>(document(), *this, move(style));
 }
 
-void HTMLIFrameElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLIFrameElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
     if (name == HTML::AttributeNames::src)
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.h b/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.h
index 95a24d1e835..d10dd68e305 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLIFrameElement.h
@@ -31,7 +31,7 @@ private:
     // ^DOM::Element
     virtual void inserted() override;
     virtual void removed_from(Node*) override;
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
     virtual i32 default_tab_index_value() const override;
 
     // https://html.spec.whatwg.org/multipage/iframe-embed-object.html#process-the-iframe-attributes
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp
index 55cb5e47371..411717ee0bf 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp
@@ -73,7 +73,7 @@ void HTMLImageElement::apply_presentational_hints(CSS::StyleProperties& style) c
     });
 }
 
-void HTMLImageElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLImageElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
 
@@ -198,7 +198,7 @@ bool HTMLImageElement::complete() const
     return false;
 }
 
-FlyString HTMLImageElement::default_role() const
+DeprecatedFlyString HTMLImageElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-img
     // https://www.w3.org/TR/html-aria/#el-img-no-alt
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLImageElement.h b/Userland/Libraries/LibWeb/HTML/HTMLImageElement.h
index ee72cfa1ab4..94b6d8a5c54 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLImageElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLImageElement.h
@@ -24,7 +24,7 @@ class HTMLImageElement final
 public:
     virtual ~HTMLImageElement() override;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     DeprecatedString alt() const { return attribute(HTML::AttributeNames::alt); }
     DeprecatedString src() const { return attribute(HTML::AttributeNames::src); }
@@ -43,7 +43,7 @@ public:
     // https://html.spec.whatwg.org/multipage/embedded-content.html#dom-img-complete
     bool complete() const;
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLImageElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp
index ae20f490aaa..3c20012d638 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLInputElement.cpp
@@ -404,7 +404,7 @@ void HTMLInputElement::did_receive_focus()
     browsing_context->set_cursor_position(DOM::Position { *m_text_node, 0 });
 }
 
-void HTMLInputElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLInputElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
     if (name == HTML::AttributeNames::checked) {
@@ -434,7 +434,7 @@ HTMLInputElement::TypeAttributeState HTMLInputElement::parse_type_attribute(Stri
     return HTMLInputElement::TypeAttributeState::Text;
 }
 
-void HTMLInputElement::did_remove_attribute(FlyString const& name)
+void HTMLInputElement::did_remove_attribute(DeprecatedFlyString const& name)
 {
     HTMLElement::did_remove_attribute(name);
     if (name == HTML::AttributeNames::checked) {
@@ -866,7 +866,7 @@ WebIDL::ExceptionOr<void> HTMLInputElement::set_selection_range(u32 start, u32 e
     return {};
 }
 
-FlyString HTMLInputElement::default_role() const
+DeprecatedFlyString HTMLInputElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-input-button
     if (type_state() == TypeAttributeState::Button)
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLInputElement.h b/Userland/Libraries/LibWeb/HTML/HTMLInputElement.h
index 8bb9b4ee2fe..f9e0b369dc6 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLInputElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLInputElement.h
@@ -96,8 +96,8 @@ public:
     virtual bool is_focusable() const override { return m_type != TypeAttributeState::Hidden; }
 
     // ^HTMLElement
-    virtual void parse_attribute(FlyString const&, DeprecatedString const&) override;
-    virtual void did_remove_attribute(FlyString const&) override;
+    virtual void parse_attribute(DeprecatedFlyString const&, DeprecatedString const&) override;
+    virtual void did_remove_attribute(DeprecatedFlyString const&) override;
 
     // ^FormAssociatedElement
     // https://html.spec.whatwg.org/multipage/forms.html#category-listed
@@ -120,7 +120,7 @@ public:
     // https://html.spec.whatwg.org/multipage/forms.html#category-label
     virtual bool is_labelable() const override { return type_state() != TypeAttributeState::Hidden; }
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLInputElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLLIElement.h b/Userland/Libraries/LibWeb/HTML/HTMLLIElement.h
index 6b5ed2b23e7..082670302ae 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLLIElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLLIElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLLIElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-li
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::listitem; };
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::listitem; };
 
 private:
     HTMLLIElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
index cde4f0f0630..e0f657d2466 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.cpp
@@ -69,7 +69,7 @@ bool HTMLLinkElement::has_loaded_icon() const
     return m_relationship & Relationship::Icon && resource() && resource()->is_loaded() && resource()->has_encoded_data();
 }
 
-void HTMLLinkElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLLinkElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     // 4.6.7 Link types - https://html.spec.whatwg.org/multipage/links.html#linkTypes
     if (name == HTML::AttributeNames::rel) {
@@ -118,7 +118,7 @@ void HTMLLinkElement::resource_did_load()
         resource_did_load_favicon();
 }
 
-void HTMLLinkElement::did_remove_attribute(FlyString const& attr)
+void HTMLLinkElement::did_remove_attribute(DeprecatedFlyString const& attr)
 {
     if (attr == HTML::AttributeNames::disabled && (m_relationship & Relationship::Stylesheet)) {
         if (!resource())
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
index adbbfe6e574..73edcfe1376 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h
@@ -33,14 +33,14 @@ public:
 private:
     HTMLLinkElement(DOM::Document&, DOM::QualifiedName);
 
-    void parse_attribute(FlyString const&, DeprecatedString const&) override;
+    void parse_attribute(DeprecatedFlyString const&, DeprecatedString const&) override;
 
     // ^ResourceClient
     virtual void resource_did_fail() override;
     virtual void resource_did_load() override;
 
     // ^ HTMLElement
-    virtual void did_remove_attribute(FlyString const&) override;
+    virtual void did_remove_attribute(DeprecatedFlyString const&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
     void resource_did_load_stylesheet();
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLMenuElement.h b/Userland/Libraries/LibWeb/HTML/HTMLMenuElement.h
index fffd6749651..7517b6a9272 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLMenuElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLMenuElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLMenuElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-menu
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::list; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::list; }
 
 private:
     HTMLMenuElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLMeterElement.h b/Userland/Libraries/LibWeb/HTML/HTMLMeterElement.h
index 86a6880eff0..9bb413df888 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLMeterElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLMeterElement.h
@@ -23,7 +23,7 @@ public:
     virtual bool is_labelable() const override { return true; }
 
     // https://www.w3.org/TR/html-aria/#el-meter
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::meter; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::meter; }
 
 private:
     HTMLMeterElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLModElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLModElement.cpp
index 60ce086bc12..b8326ea34a3 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLModElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLModElement.cpp
@@ -18,7 +18,7 @@ HTMLModElement::HTMLModElement(DOM::Document& document, DOM::QualifiedName quali
 
 HTMLModElement::~HTMLModElement() = default;
 
-FlyString HTMLModElement::default_role() const
+DeprecatedFlyString HTMLModElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-del
     if (local_name() == TagNames::del)
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLModElement.h b/Userland/Libraries/LibWeb/HTML/HTMLModElement.h
index 2dbc748a8e3..908f56c12f2 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLModElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLModElement.h
@@ -17,7 +17,7 @@ class HTMLModElement final : public HTMLElement {
 public:
     virtual ~HTMLModElement() override;
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLModElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLOListElement.h b/Userland/Libraries/LibWeb/HTML/HTMLOListElement.h
index 9ff8034f245..81f63c1247d 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLOListElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLOListElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLOListElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-ol
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::list; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::list; }
 
 private:
     HTMLOListElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.cpp
index cfdc8dcfbf0..68a1a1c87fa 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.cpp
@@ -32,7 +32,7 @@ HTMLObjectElement::HTMLObjectElement(DOM::Document& document, DOM::QualifiedName
 
 HTMLObjectElement::~HTMLObjectElement() = default;
 
-void HTMLObjectElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLObjectElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     BrowsingContextContainer::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.h b/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.h
index de5bb2d80ec..a83ecafc4d5 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLObjectElement.h
@@ -32,7 +32,7 @@ class HTMLObjectElement final
 public:
     virtual ~HTMLObjectElement() override;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     DeprecatedString data() const;
     void set_data(DeprecatedString const& data) { MUST(set_attribute(HTML::AttributeNames::data, data)); }
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLOptGroupElement.h b/Userland/Libraries/LibWeb/HTML/HTMLOptGroupElement.h
index 708c09ad1bc..d6875b1dc65 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLOptGroupElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLOptGroupElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLOptGroupElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-optgroup
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::group; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::group; }
 
 private:
     HTMLOptGroupElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp
index 4396f9d9cf1..9c2cfc224d3 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.cpp
@@ -26,7 +26,7 @@ HTMLOptionElement::HTMLOptionElement(DOM::Document& document, DOM::QualifiedName
 
 HTMLOptionElement::~HTMLOptionElement() = default;
 
-void HTMLOptionElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void HTMLOptionElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     HTMLElement::parse_attribute(name, value);
 
@@ -39,7 +39,7 @@ void HTMLOptionElement::parse_attribute(FlyString const& name, DeprecatedString
     }
 }
 
-void HTMLOptionElement::did_remove_attribute(FlyString const& name)
+void HTMLOptionElement::did_remove_attribute(DeprecatedFlyString const& name)
 {
     HTMLElement::did_remove_attribute(name);
 
@@ -141,7 +141,7 @@ bool HTMLOptionElement::disabled() const
         || (parent() && is<HTMLOptGroupElement>(parent()) && static_cast<HTMLOptGroupElement const&>(*parent()).has_attribute(AttributeNames::disabled));
 }
 
-FlyString HTMLOptionElement::default_role() const
+DeprecatedFlyString HTMLOptionElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-option
     // TODO: Only an option element that is in a list of options or that represents a suggestion in a datalist should return option
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h b/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h
index 2083fc30bc7..1f0c9546ea5 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLOptionElement.h
@@ -30,7 +30,7 @@ public:
 
     bool disabled() const;
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     friend class Bindings::OptionConstructor;
@@ -38,8 +38,8 @@ private:
 
     HTMLOptionElement(DOM::Document&, DOM::QualifiedName);
 
-    void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
-    void did_remove_attribute(FlyString const& name) override;
+    void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
+    void did_remove_attribute(DeprecatedFlyString const& name) override;
 
     void ask_for_a_reset();
 
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLOutputElement.h b/Userland/Libraries/LibWeb/HTML/HTMLOutputElement.h
index 0012795625c..9d46c7d8b6f 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLOutputElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLOutputElement.h
@@ -45,7 +45,7 @@ public:
     virtual void reset_algorithm() override;
 
     // https://www.w3.org/TR/html-aria/#el-output
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::status; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::status; }
 
 private:
     HTMLOutputElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLParagraphElement.h b/Userland/Libraries/LibWeb/HTML/HTMLParagraphElement.h
index 6c2cb0cae74..e0572366ec6 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLParagraphElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLParagraphElement.h
@@ -20,7 +20,7 @@ public:
     virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
     // https://www.w3.org/TR/html-aria/#el-p
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::paragraph; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::paragraph; }
 
 private:
     HTMLParagraphElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLPreElement.h b/Userland/Libraries/LibWeb/HTML/HTMLPreElement.h
index bf7f793df39..bfb623ab529 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLPreElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLPreElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLPreElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-pre
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::generic; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::generic; }
 
 private:
     HTMLPreElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLProgressElement.h b/Userland/Libraries/LibWeb/HTML/HTMLProgressElement.h
index 9e51af0d508..00689839f53 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLProgressElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLProgressElement.h
@@ -34,7 +34,7 @@ public:
     bool using_system_appearance() const;
 
     // https://www.w3.org/TR/html-aria/#el-progress
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::progressbar; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::progressbar; }
 
 private:
     HTMLProgressElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.cpp
index 6bca0b337b0..116842758e8 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.cpp
@@ -19,7 +19,7 @@ HTMLQuoteElement::HTMLQuoteElement(DOM::Document& document, DOM::QualifiedName q
 
 HTMLQuoteElement::~HTMLQuoteElement() = default;
 
-FlyString HTMLQuoteElement::default_role() const
+DeprecatedFlyString HTMLQuoteElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-blockquote
     if (local_name() == TagNames::blockquote)
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.h b/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.h
index da36f18ce6a..79748de6f33 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLQuoteElement.h
@@ -16,7 +16,7 @@ class HTMLQuoteElement final : public HTMLElement {
 public:
     virtual ~HTMLQuoteElement() override;
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLQuoteElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp
index 29d23803a63..5ed7612b836 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp
@@ -57,7 +57,7 @@ DOM::Element* HTMLSelectElement::item(size_t index)
 }
 
 // https://html.spec.whatwg.org/multipage/form-elements.html#dom-select-nameditem
-DOM::Element* HTMLSelectElement::named_item(FlyString const& name)
+DOM::Element* HTMLSelectElement::named_item(DeprecatedFlyString const& name)
 {
     // The namedItem(name) method must return the value returned by the method of the same name on the options collection, when invoked with the same argument.
     return const_cast<HTMLOptionsCollection&>(*options()).named_item(name);
@@ -156,7 +156,7 @@ DeprecatedString const& HTMLSelectElement::type() const
     return select_multiple;
 }
 
-FlyString HTMLSelectElement::default_role() const
+DeprecatedFlyString HTMLSelectElement::default_role() const
 {
     // https://www.w3.org/TR/html-aria/#el-select-multiple-or-size-greater-1
     if (has_attribute("multiple"))
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h b/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h
index d08e9bd69de..0e1c211bdab 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLSelectElement.h
@@ -27,7 +27,7 @@ public:
 
     size_t length();
     DOM::Element* item(size_t index);
-    DOM::Element* named_item(FlyString const& name);
+    DOM::Element* named_item(DeprecatedFlyString const& name);
     WebIDL::ExceptionOr<void> add(HTMLOptionOrOptGroupElement element, Optional<HTMLElementOrElementIndex> before = {});
 
     int selected_index() const;
@@ -60,7 +60,7 @@ public:
 
     DeprecatedString const& type() const;
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLSelectElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLSpanElement.h b/Userland/Libraries/LibWeb/HTML/HTMLSpanElement.h
index 3a3faf3df21..75e165fcad7 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLSpanElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLSpanElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLSpanElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-span
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::generic; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::generic; }
 
 private:
     HTMLSpanElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableCaptionElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTableCaptionElement.h
index 3393faadf39..259dbb101d8 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableCaptionElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableCaptionElement.h
@@ -20,7 +20,7 @@ public:
     virtual void apply_presentational_hints(CSS::StyleProperties&) const override;
 
     // https://www.w3.org/TR/html-aria/#el-caption
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::caption; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::caption; }
 
 private:
     HTMLTableCaptionElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.cpp b/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.cpp
index 0b4c2d3df26..a97862b517f 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.cpp
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.cpp
@@ -69,7 +69,7 @@ void HTMLTableCellElement::set_row_span(unsigned int value)
     MUST(set_attribute(HTML::AttributeNames::rowspan, DeprecatedString::number(value)));
 }
 
-FlyString HTMLTableCellElement::default_role() const
+DeprecatedFlyString HTMLTableCellElement::default_role() const
 {
     // TODO: For td:
     //       role=cell if the ancestor table element is exposed as a role=table
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.h
index 53e281073dd..c3e02ded3bb 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableCellElement.h
@@ -22,7 +22,7 @@ public:
     void set_col_span(unsigned);
     void set_row_span(unsigned);
 
-    virtual FlyString default_role() const override;
+    virtual DeprecatedFlyString default_role() const override;
 
 private:
     HTMLTableCellElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTableElement.h
index cf36ec6934e..40b8eff6820 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableElement.h
@@ -43,7 +43,7 @@ public:
     WebIDL::ExceptionOr<void> delete_row(long index);
 
     // https://www.w3.org/TR/html-aria/#el-table
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::table; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::table; }
 
 private:
     HTMLTableElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableRowElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTableRowElement.h
index ee3fc521d9c..ea80fe5bc2a 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableRowElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableRowElement.h
@@ -25,7 +25,7 @@ public:
     WebIDL::ExceptionOr<void> delete_cell(i32 index);
 
     // https://www.w3.org/TR/html-aria/#el-tr
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::row; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::row; }
 
 private:
     HTMLTableRowElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h
index 083654b99d9..025ff5a8746 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTableSectionElement.h
@@ -25,7 +25,7 @@ public:
     // https://www.w3.org/TR/html-aria/#el-tbody
     // https://www.w3.org/TR/html-aria/#el-tfoot
     // https://www.w3.org/TR/html-aria/#el-thead
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::rowgroup; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::rowgroup; }
 
 private:
     HTMLTableSectionElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h
index 939ec8fe85c..7b5af5691f7 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTextAreaElement.h
@@ -52,7 +52,7 @@ public:
     virtual void reset_algorithm() override;
 
     // https://www.w3.org/TR/html-aria/#el-textarea
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::textbox; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::textbox; }
 
 private:
     HTMLTextAreaElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLTimeElement.h b/Userland/Libraries/LibWeb/HTML/HTMLTimeElement.h
index 3272d313091..f6962c6695a 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLTimeElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLTimeElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLTimeElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-time
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::time; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::time; }
 
 private:
     HTMLTimeElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/HTMLUListElement.h b/Userland/Libraries/LibWeb/HTML/HTMLUListElement.h
index 5af03e87979..9c7b275f5c9 100644
--- a/Userland/Libraries/LibWeb/HTML/HTMLUListElement.h
+++ b/Userland/Libraries/LibWeb/HTML/HTMLUListElement.h
@@ -18,7 +18,7 @@ public:
     virtual ~HTMLUListElement() override;
 
     // https://www.w3.org/TR/html-aria/#el-ul
-    virtual FlyString default_role() const override { return DOM::ARIARoleNames::list; }
+    virtual DeprecatedFlyString default_role() const override { return DOM::ARIARoleNames::list; }
 
 private:
     HTMLUListElement(DOM::Document&, DOM::QualifiedName);
diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp b/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
index 35160737207..907b8691141 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-MessageEvent* MessageEvent::create(JS::Realm& realm, FlyString const& event_name, MessageEventInit const& event_init)
+MessageEvent* MessageEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, MessageEventInit const& event_init)
 {
     return realm.heap().allocate<MessageEvent>(realm, realm, event_name, event_init);
 }
 
-MessageEvent* MessageEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, MessageEventInit const& event_init)
+MessageEvent* MessageEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, MessageEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-MessageEvent::MessageEvent(JS::Realm& realm, FlyString const& event_name, MessageEventInit const& event_init)
+MessageEvent::MessageEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, MessageEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_data(event_init.data)
     , m_origin(event_init.origin)
diff --git a/Userland/Libraries/LibWeb/HTML/MessageEvent.h b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
index b8c4fbd6395..675c1eeffe4 100644
--- a/Userland/Libraries/LibWeb/HTML/MessageEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/MessageEvent.h
@@ -21,10 +21,10 @@ class MessageEvent : public DOM::Event {
     WEB_PLATFORM_OBJECT(MessageEvent, DOM::Event);
 
 public:
-    static MessageEvent* create(JS::Realm&, FlyString const& event_name, MessageEventInit const& event_init = {});
-    static MessageEvent* construct_impl(JS::Realm&, FlyString const& event_name, MessageEventInit const& event_init);
+    static MessageEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, MessageEventInit const& event_init = {});
+    static MessageEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, MessageEventInit const& event_init);
 
-    MessageEvent(JS::Realm&, FlyString const& event_name, MessageEventInit const& event_init);
+    MessageEvent(JS::Realm&, DeprecatedFlyString const& event_name, MessageEventInit const& event_init);
     virtual ~MessageEvent() override;
 
     JS::Value data() const { return m_data; }
diff --git a/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.cpp b/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.cpp
index bf577ea81af..177277ffa4d 100644
--- a/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-PageTransitionEvent* PageTransitionEvent::create(JS::Realm& realm, FlyString const& event_name, PageTransitionEventInit const& event_init)
+PageTransitionEvent* PageTransitionEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init)
 {
     return realm.heap().allocate<PageTransitionEvent>(realm, realm, event_name, event_init);
 }
 
-PageTransitionEvent* PageTransitionEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, PageTransitionEventInit const& event_init)
+PageTransitionEvent* PageTransitionEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-PageTransitionEvent::PageTransitionEvent(JS::Realm& realm, FlyString const& event_name, PageTransitionEventInit const& event_init)
+PageTransitionEvent::PageTransitionEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_persisted(event_init.persisted)
 {
diff --git a/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.h b/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.h
index 172df453c01..e809bc9f598 100644
--- a/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/PageTransitionEvent.h
@@ -18,10 +18,10 @@ class PageTransitionEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(PageTransitionEvent, DOM::Event);
 
 public:
-    static PageTransitionEvent* create(JS::Realm&, FlyString const& event_name, PageTransitionEventInit const& event_init);
-    static PageTransitionEvent* construct_impl(JS::Realm&, FlyString const& event_name, PageTransitionEventInit const& event_init);
+    static PageTransitionEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init);
+    static PageTransitionEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init);
 
-    PageTransitionEvent(JS::Realm&, FlyString const& event_name, PageTransitionEventInit const& event_init);
+    PageTransitionEvent(JS::Realm&, DeprecatedFlyString const& event_name, PageTransitionEventInit const& event_init);
 
     virtual ~PageTransitionEvent() override;
 
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp b/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp
index 8194593d14c..78878c422a5 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp
@@ -40,7 +40,7 @@ static inline void log_parse_error(SourceLocation const& location = SourceLocati
     dbgln_if(HTML_PARSER_DEBUG, "Parse error! {}", location);
 }
 
-static Vector<FlyString> s_quirks_public_ids = {
+static Vector<DeprecatedFlyString> s_quirks_public_ids = {
     "+//Silmaril//dtd html Pro v0r11 19970101//",
     "-//AS//DTD HTML 3.0 asWedit + extensions//",
     "-//AdvaSoft Ltd//DTD HTML 3.0 asWedit + extensions//",
@@ -616,7 +616,7 @@ HTMLParser::AdjustedInsertionLocation HTMLParser::find_appropriate_place_for_ins
     return adjusted_insertion_location;
 }
 
-JS::NonnullGCPtr<DOM::Element> HTMLParser::create_element_for(HTMLToken const& token, FlyString const& namespace_, DOM::Node const& intended_parent)
+JS::NonnullGCPtr<DOM::Element> HTMLParser::create_element_for(HTMLToken const& token, DeprecatedFlyString const& namespace_, DOM::Node const& intended_parent)
 {
     // FIXME: 1. If the active speculative HTML parser is not null, then return the result of creating a speculative mock element given given namespace, the tag name of the given token, and the attributes of the given token.
     // FIXME: 2. Otherwise, optionally create a speculative mock element given given namespace, the tag name of the given token, and the attributes of the given token.
@@ -681,7 +681,7 @@ JS::NonnullGCPtr<DOM::Element> HTMLParser::create_element_for(HTMLToken const& t
 }
 
 // https://html.spec.whatwg.org/multipage/parsing.html#insert-a-foreign-element
-JS::NonnullGCPtr<DOM::Element> HTMLParser::insert_foreign_element(HTMLToken const& token, FlyString const& namespace_)
+JS::NonnullGCPtr<DOM::Element> HTMLParser::insert_foreign_element(HTMLToken const& token, DeprecatedFlyString const& namespace_)
 {
     auto adjusted_insertion_location = find_appropriate_place_for_inserting_node();
 
@@ -1041,7 +1041,7 @@ AnythingElse:
     process_using_the_rules_for(m_insertion_mode, token);
 }
 
-void HTMLParser::generate_implied_end_tags(FlyString const& exception)
+void HTMLParser::generate_implied_end_tags(DeprecatedFlyString const& exception)
 {
     while (current_node().local_name() != exception && current_node().local_name().is_one_of(HTML::TagNames::dd, HTML::TagNames::dt, HTML::TagNames::li, HTML::TagNames::optgroup, HTML::TagNames::option, HTML::TagNames::p, HTML::TagNames::rb, HTML::TagNames::rp, HTML::TagNames::rt, HTML::TagNames::rtc))
         (void)m_stack_of_open_elements.pop();
@@ -1365,7 +1365,7 @@ HTMLParser::AdoptionAgencyAlgorithmOutcome HTMLParser::run_the_adoption_agency_a
     }
 }
 
-bool HTMLParser::is_special_tag(FlyString const& tag_name, FlyString const& namespace_)
+bool HTMLParser::is_special_tag(DeprecatedFlyString const& tag_name, DeprecatedFlyString const& namespace_)
 {
     if (namespace_ == Namespace::HTML) {
         return tag_name.is_one_of(
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.h b/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.h
index d535dee9eaa..1fc9841b9e2 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.h
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.h
@@ -67,7 +67,7 @@ public:
 
     InsertionMode insertion_mode() const { return m_insertion_mode; }
 
-    static bool is_special_tag(FlyString const& tag_name, FlyString const& namespace_);
+    static bool is_special_tag(DeprecatedFlyString const& tag_name, DeprecatedFlyString const& namespace_);
 
     HTMLTokenizer& tokenizer() { return m_tokenizer; }
 
@@ -117,9 +117,9 @@ private:
 
     void stop_parsing() { m_stop_parsing = true; }
 
-    void generate_implied_end_tags(FlyString const& exception = {});
+    void generate_implied_end_tags(DeprecatedFlyString const& exception = {});
     void generate_all_implied_end_tags_thoroughly();
-    JS::NonnullGCPtr<DOM::Element> create_element_for(HTMLToken const&, FlyString const& namespace_, DOM::Node const& intended_parent);
+    JS::NonnullGCPtr<DOM::Element> create_element_for(HTMLToken const&, DeprecatedFlyString const& namespace_, DOM::Node const& intended_parent);
 
     struct AdjustedInsertionLocation {
         JS::GCPtr<DOM::Node> parent;
@@ -130,7 +130,7 @@ private:
 
     DOM::Text* find_character_insertion_node();
     void flush_character_insertions();
-    JS::NonnullGCPtr<DOM::Element> insert_foreign_element(HTMLToken const&, FlyString const&);
+    JS::NonnullGCPtr<DOM::Element> insert_foreign_element(HTMLToken const&, DeprecatedFlyString const&);
     JS::NonnullGCPtr<DOM::Element> insert_html_element(HTMLToken const&);
     DOM::Element& current_node();
     DOM::Element& adjusted_current_node();
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h b/Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h
index d42562d7741..c49d98ab658 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h
+++ b/Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h
@@ -7,8 +7,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/DeprecatedString.h>
-#include <AK/FlyString.h>
 #include <AK/Function.h>
 #include <AK/OwnPtr.h>
 #include <AK/Types.h>
@@ -67,7 +67,7 @@ public:
         return token;
     }
 
-    static HTMLToken make_start_tag(FlyString const& tag_name)
+    static HTMLToken make_start_tag(DeprecatedFlyString const& tag_name)
     {
         HTMLToken token { Type::StartTag };
         token.set_tag_name(tag_name);
@@ -134,7 +134,7 @@ public:
         m_data.get<u32>() = code_point;
     }
 
-    FlyString const& comment() const
+    DeprecatedFlyString const& comment() const
     {
         VERIFY(is_comment());
         return m_string_data;
@@ -146,7 +146,7 @@ public:
         m_string_data = move(comment);
     }
 
-    FlyString const& tag_name() const
+    DeprecatedFlyString const& tag_name() const
     {
         VERIFY(is_start_tag() || is_end_tag());
         return m_string_data;
@@ -247,7 +247,7 @@ public:
         }
     }
 
-    StringView attribute(FlyString const& attribute_name)
+    StringView attribute(DeprecatedFlyString const& attribute_name)
     {
         VERIFY(is_start_tag() || is_end_tag());
 
@@ -261,19 +261,19 @@ public:
         return {};
     }
 
-    bool has_attribute(FlyString const& attribute_name)
+    bool has_attribute(DeprecatedFlyString const& attribute_name)
     {
         return !attribute(attribute_name).is_null();
     }
 
-    void adjust_tag_name(FlyString const& old_name, FlyString const& new_name)
+    void adjust_tag_name(DeprecatedFlyString const& old_name, DeprecatedFlyString const& new_name)
     {
         VERIFY(is_start_tag() || is_end_tag());
         if (old_name == tag_name())
             set_tag_name(new_name);
     }
 
-    void adjust_attribute_name(FlyString const& old_name, FlyString const& new_name)
+    void adjust_attribute_name(DeprecatedFlyString const& old_name, DeprecatedFlyString const& new_name)
     {
         VERIFY(is_start_tag() || is_end_tag());
         for_each_attribute([&](Attribute& attribute) {
@@ -283,7 +283,7 @@ public:
         });
     }
 
-    void adjust_foreign_attribute(FlyString const& old_name, FlyString const& prefix, FlyString const& local_name, FlyString const& namespace_)
+    void adjust_foreign_attribute(DeprecatedFlyString const& old_name, DeprecatedFlyString const& prefix, DeprecatedFlyString const& local_name, DeprecatedFlyString const& namespace_)
     {
         VERIFY(is_start_tag() || is_end_tag());
         for_each_attribute([&](Attribute& attribute) {
@@ -350,7 +350,7 @@ private:
     bool m_tag_self_closing_acknowledged { false };
 
     // Type::Comment (comment data), Type::StartTag and Type::EndTag (tag name)
-    FlyString m_string_data;
+    DeprecatedFlyString m_string_data;
 
     Variant<Empty, u32, OwnPtr<DoctypeData>, OwnPtr<Vector<Attribute>>> m_data {};
 
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.cpp b/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.cpp
index 91d842f7c55..c454173227d 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.cpp
@@ -37,7 +37,7 @@ bool ListOfActiveFormattingElements::contains(const DOM::Element& element) const
     return false;
 }
 
-DOM::Element* ListOfActiveFormattingElements::last_element_with_tag_name_before_marker(FlyString const& tag_name)
+DOM::Element* ListOfActiveFormattingElements::last_element_with_tag_name_before_marker(DeprecatedFlyString const& tag_name)
 {
     for (ssize_t i = m_entries.size() - 1; i >= 0; --i) {
         auto& entry = m_entries[i];
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.h b/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.h
index 661a6094d58..046b82b4aa5 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.h
+++ b/Userland/Libraries/LibWeb/HTML/Parser/ListOfActiveFormattingElements.h
@@ -37,7 +37,7 @@ public:
     Vector<Entry> const& entries() const { return m_entries; }
     Vector<Entry>& entries() { return m_entries; }
 
-    DOM::Element* last_element_with_tag_name_before_marker(FlyString const& tag_name);
+    DOM::Element* last_element_with_tag_name_before_marker(DeprecatedFlyString const& tag_name);
 
     void clear_up_to_the_last_marker();
 
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.cpp b/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.cpp
index ab9906c262d..93bcfd6cd59 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.cpp
@@ -10,7 +10,7 @@
 
 namespace Web::HTML {
 
-static Vector<FlyString> s_base_list { "applet", "caption", "html", "table", "td", "th", "marquee", "object", "template" };
+static Vector<DeprecatedFlyString> s_base_list { "applet", "caption", "html", "table", "td", "th", "marquee", "object", "template" };
 
 StackOfOpenElements::~StackOfOpenElements() = default;
 
@@ -20,7 +20,7 @@ void StackOfOpenElements::visit_edges(JS::Cell::Visitor& visitor)
         visitor.visit(element);
 }
 
-bool StackOfOpenElements::has_in_scope_impl(FlyString const& tag_name, Vector<FlyString> const& list) const
+bool StackOfOpenElements::has_in_scope_impl(DeprecatedFlyString const& tag_name, Vector<DeprecatedFlyString> const& list) const
 {
     for (auto const& element : m_elements.in_reverse()) {
         if (element->local_name() == tag_name)
@@ -31,12 +31,12 @@ bool StackOfOpenElements::has_in_scope_impl(FlyString const& tag_name, Vector<Fl
     VERIFY_NOT_REACHED();
 }
 
-bool StackOfOpenElements::has_in_scope(FlyString const& tag_name) const
+bool StackOfOpenElements::has_in_scope(DeprecatedFlyString const& tag_name) const
 {
     return has_in_scope_impl(tag_name, s_base_list);
 }
 
-bool StackOfOpenElements::has_in_scope_impl(const DOM::Element& target_node, Vector<FlyString> const& list) const
+bool StackOfOpenElements::has_in_scope_impl(const DOM::Element& target_node, Vector<DeprecatedFlyString> const& list) const
 {
     for (auto& element : m_elements.in_reverse()) {
         if (element.ptr() == &target_node)
@@ -52,19 +52,19 @@ bool StackOfOpenElements::has_in_scope(const DOM::Element& target_node) const
     return has_in_scope_impl(target_node, s_base_list);
 }
 
-bool StackOfOpenElements::has_in_button_scope(FlyString const& tag_name) const
+bool StackOfOpenElements::has_in_button_scope(DeprecatedFlyString const& tag_name) const
 {
     auto list = s_base_list;
     list.append("button");
     return has_in_scope_impl(tag_name, list);
 }
 
-bool StackOfOpenElements::has_in_table_scope(FlyString const& tag_name) const
+bool StackOfOpenElements::has_in_table_scope(DeprecatedFlyString const& tag_name) const
 {
     return has_in_scope_impl(tag_name, { "html", "table", "template" });
 }
 
-bool StackOfOpenElements::has_in_list_item_scope(FlyString const& tag_name) const
+bool StackOfOpenElements::has_in_list_item_scope(DeprecatedFlyString const& tag_name) const
 {
     auto list = s_base_list;
     list.append("ol");
@@ -78,7 +78,7 @@ bool StackOfOpenElements::has_in_list_item_scope(FlyString const& tag_name) cons
 // - optgroup in the HTML namespace
 // - option in the HTML namespace
 // NOTE: In this case it's "all element types _except_"
-bool StackOfOpenElements::has_in_select_scope(FlyString const& tag_name) const
+bool StackOfOpenElements::has_in_select_scope(DeprecatedFlyString const& tag_name) const
 {
     // https://html.spec.whatwg.org/multipage/parsing.html#has-an-element-in-the-specific-scope
     // 1. Initialize node to be the current node (the bottommost node of the stack).
@@ -106,7 +106,7 @@ bool StackOfOpenElements::contains(const DOM::Element& element) const
     return false;
 }
 
-bool StackOfOpenElements::contains(FlyString const& tag_name) const
+bool StackOfOpenElements::contains(DeprecatedFlyString const& tag_name) const
 {
     for (auto& element_on_stack : m_elements) {
         if (element_on_stack->local_name() == tag_name)
@@ -115,7 +115,7 @@ bool StackOfOpenElements::contains(FlyString const& tag_name) const
     return false;
 }
 
-void StackOfOpenElements::pop_until_an_element_with_tag_name_has_been_popped(FlyString const& tag_name)
+void StackOfOpenElements::pop_until_an_element_with_tag_name_has_been_popped(DeprecatedFlyString const& tag_name)
 {
     while (m_elements.last()->local_name() != tag_name)
         (void)pop();
@@ -134,7 +134,7 @@ JS::GCPtr<DOM::Element> StackOfOpenElements::topmost_special_node_below(DOM::Ele
     return found_element.ptr();
 }
 
-StackOfOpenElements::LastElementResult StackOfOpenElements::last_element_with_tag_name(FlyString const& tag_name)
+StackOfOpenElements::LastElementResult StackOfOpenElements::last_element_with_tag_name(DeprecatedFlyString const& tag_name)
 {
     for (ssize_t i = m_elements.size() - 1; i >= 0; --i) {
         auto& element = m_elements[i];
diff --git a/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.h b/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.h
index d3376e36f0c..5be1c04c0bf 100644
--- a/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.h
+++ b/Userland/Libraries/LibWeb/HTML/Parser/StackOfOpenElements.h
@@ -36,21 +36,21 @@ public:
     const DOM::Element& current_node() const { return *m_elements.last(); }
     DOM::Element& current_node() { return *m_elements.last(); }
 
-    bool has_in_scope(FlyString const& tag_name) const;
-    bool has_in_button_scope(FlyString const& tag_name) const;
-    bool has_in_table_scope(FlyString const& tag_name) const;
-    bool has_in_list_item_scope(FlyString const& tag_name) const;
-    bool has_in_select_scope(FlyString const& tag_name) const;
+    bool has_in_scope(DeprecatedFlyString const& tag_name) const;
+    bool has_in_button_scope(DeprecatedFlyString const& tag_name) const;
+    bool has_in_table_scope(DeprecatedFlyString const& tag_name) const;
+    bool has_in_list_item_scope(DeprecatedFlyString const& tag_name) const;
+    bool has_in_select_scope(DeprecatedFlyString const& tag_name) const;
 
     bool has_in_scope(const DOM::Element&) const;
 
     bool contains(const DOM::Element&) const;
-    bool contains(FlyString const& tag_name) const;
+    bool contains(DeprecatedFlyString const& tag_name) const;
 
     auto const& elements() const { return m_elements; }
     auto& elements() { return m_elements; }
 
-    void pop_until_an_element_with_tag_name_has_been_popped(FlyString const&);
+    void pop_until_an_element_with_tag_name_has_been_popped(DeprecatedFlyString const&);
 
     JS::GCPtr<DOM::Element> topmost_special_node_below(DOM::Element const&);
 
@@ -58,14 +58,14 @@ public:
         JS::GCPtr<DOM::Element> element;
         ssize_t index;
     };
-    LastElementResult last_element_with_tag_name(FlyString const&);
+    LastElementResult last_element_with_tag_name(DeprecatedFlyString const&);
     JS::GCPtr<DOM::Element> element_immediately_above(DOM::Element const&);
 
     void visit_edges(JS::Cell::Visitor&);
 
 private:
-    bool has_in_scope_impl(FlyString const& tag_name, Vector<FlyString> const&) const;
-    bool has_in_scope_impl(const DOM::Element& target_node, Vector<FlyString> const&) const;
+    bool has_in_scope_impl(DeprecatedFlyString const& tag_name, Vector<DeprecatedFlyString> const&) const;
+    bool has_in_scope_impl(const DOM::Element& target_node, Vector<DeprecatedFlyString> const&) const;
 
     Vector<JS::NonnullGCPtr<DOM::Element>> m_elements;
 };
diff --git a/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.cpp b/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.cpp
index 075f7b351c1..f16a98a2c6d 100644
--- a/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-PromiseRejectionEvent* PromiseRejectionEvent::create(JS::Realm& realm, FlyString const& event_name, PromiseRejectionEventInit const& event_init)
+PromiseRejectionEvent* PromiseRejectionEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init)
 {
     return realm.heap().allocate<PromiseRejectionEvent>(realm, realm, event_name, event_init);
 }
 
-PromiseRejectionEvent* PromiseRejectionEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, PromiseRejectionEventInit const& event_init)
+PromiseRejectionEvent* PromiseRejectionEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-PromiseRejectionEvent::PromiseRejectionEvent(JS::Realm& realm, FlyString const& event_name, PromiseRejectionEventInit const& event_init)
+PromiseRejectionEvent::PromiseRejectionEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_promise(const_cast<JS::Promise*>(event_init.promise.cell()))
     , m_reason(event_init.reason)
diff --git a/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.h b/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
index 43029d70a09..0f79732f60e 100644
--- a/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/PromiseRejectionEvent.h
@@ -23,8 +23,8 @@ class PromiseRejectionEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(PromiseRejectionEvent, DOM::Event);
 
 public:
-    static PromiseRejectionEvent* create(JS::Realm&, FlyString const& event_name, PromiseRejectionEventInit const& event_init = {});
-    static PromiseRejectionEvent* construct_impl(JS::Realm&, FlyString const& event_name, PromiseRejectionEventInit const& event_init);
+    static PromiseRejectionEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init = {});
+    static PromiseRejectionEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init);
 
     virtual ~PromiseRejectionEvent() override;
 
@@ -33,7 +33,7 @@ public:
     JS::Value reason() const { return m_reason; }
 
 private:
-    PromiseRejectionEvent(JS::Realm&, FlyString const& event_name, PromiseRejectionEventInit const& event_init);
+    PromiseRejectionEvent(JS::Realm&, DeprecatedFlyString const& event_name, PromiseRejectionEventInit const& event_init);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
diff --git a/Userland/Libraries/LibWeb/HTML/SubmitEvent.cpp b/Userland/Libraries/LibWeb/HTML/SubmitEvent.cpp
index d1470fdacec..9d3cc07ff5f 100644
--- a/Userland/Libraries/LibWeb/HTML/SubmitEvent.cpp
+++ b/Userland/Libraries/LibWeb/HTML/SubmitEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::HTML {
 
-SubmitEvent* SubmitEvent::create(JS::Realm& realm, FlyString const& event_name, SubmitEventInit const& event_init)
+SubmitEvent* SubmitEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init)
 {
     return realm.heap().allocate<SubmitEvent>(realm, realm, event_name, event_init);
 }
 
-SubmitEvent* SubmitEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, SubmitEventInit const& event_init)
+SubmitEvent* SubmitEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-SubmitEvent::SubmitEvent(JS::Realm& realm, FlyString const& event_name, SubmitEventInit const& event_init)
+SubmitEvent::SubmitEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init)
     : DOM::Event(realm, event_name, event_init)
     , m_submitter(event_init.submitter)
 {
diff --git a/Userland/Libraries/LibWeb/HTML/SubmitEvent.h b/Userland/Libraries/LibWeb/HTML/SubmitEvent.h
index 7159faa2119..56dc9b604b3 100644
--- a/Userland/Libraries/LibWeb/HTML/SubmitEvent.h
+++ b/Userland/Libraries/LibWeb/HTML/SubmitEvent.h
@@ -19,15 +19,15 @@ class SubmitEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(SubmitEvent, DOM::Event);
 
 public:
-    static SubmitEvent* create(JS::Realm&, FlyString const& event_name, SubmitEventInit const& event_init);
-    static SubmitEvent* construct_impl(JS::Realm&, FlyString const& event_name, SubmitEventInit const& event_init);
+    static SubmitEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init);
+    static SubmitEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init);
 
     virtual ~SubmitEvent() override;
 
     JS::GCPtr<HTMLElement> submitter() const { return m_submitter; }
 
 private:
-    SubmitEvent(JS::Realm&, FlyString const& event_name, SubmitEventInit const& event_init);
+    SubmitEvent(JS::Realm&, DeprecatedFlyString const& event_name, SubmitEventInit const& event_init);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
diff --git a/Userland/Libraries/LibWeb/HTML/TagNames.cpp b/Userland/Libraries/LibWeb/HTML/TagNames.cpp
index 732bdae01f9..435755b9f2c 100644
--- a/Userland/Libraries/LibWeb/HTML/TagNames.cpp
+++ b/Userland/Libraries/LibWeb/HTML/TagNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::HTML::TagNames {
 
-#define __ENUMERATE_HTML_TAG(name) FlyString name;
+#define __ENUMERATE_HTML_TAG(name) DeprecatedFlyString name;
 ENUMERATE_HTML_TAGS
 #undef __ENUMERATE_HTML_TAG
 
diff --git a/Userland/Libraries/LibWeb/HTML/TagNames.h b/Userland/Libraries/LibWeb/HTML/TagNames.h
index 77e25145e8c..e8fb8dd0497 100644
--- a/Userland/Libraries/LibWeb/HTML/TagNames.h
+++ b/Userland/Libraries/LibWeb/HTML/TagNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::HTML::TagNames {
 
@@ -152,7 +152,7 @@ namespace Web::HTML::TagNames {
     __ENUMERATE_HTML_TAG(wbr)        \
     __ENUMERATE_HTML_TAG(xmp)
 
-#define __ENUMERATE_HTML_TAG(name) extern FlyString name;
+#define __ENUMERATE_HTML_TAG(name) extern DeprecatedFlyString name;
 ENUMERATE_HTML_TAGS
 #undef __ENUMERATE_HTML_TAG
 
diff --git a/Userland/Libraries/LibWeb/HTML/Window.cpp b/Userland/Libraries/LibWeb/HTML/Window.cpp
index a32837627ef..f00a8cccdad 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Window.cpp
@@ -780,7 +780,7 @@ float Window::scroll_y() const
 }
 
 // https://html.spec.whatwg.org/#fire-a-page-transition-event
-void Window::fire_a_page_transition_event(FlyString const& event_name, bool persisted)
+void Window::fire_a_page_transition_event(DeprecatedFlyString const& event_name, bool persisted)
 {
     // To fire a page transition event named eventName at a Window window with a boolean persisted,
     // fire an event named eventName at window, using PageTransitionEvent,
diff --git a/Userland/Libraries/LibWeb/HTML/Window.h b/Userland/Libraries/LibWeb/HTML/Window.h
index fc713fcf2e8..1cf75d254e6 100644
--- a/Userland/Libraries/LibWeb/HTML/Window.h
+++ b/Userland/Libraries/LibWeb/HTML/Window.h
@@ -102,7 +102,7 @@ public:
     float scroll_x() const;
     float scroll_y() const;
 
-    void fire_a_page_transition_event(FlyString const& event_name, bool persisted);
+    void fire_a_page_transition_event(DeprecatedFlyString const& event_name, bool persisted);
 
     float device_pixel_ratio() const;
 
@@ -142,7 +142,7 @@ private:
     virtual void visit_edges(Cell::Visitor&) override;
 
     // ^HTML::GlobalEventHandlers
-    virtual DOM::EventTarget& global_event_handlers_to_event_target(FlyString const&) override { return *this; }
+    virtual DOM::EventTarget& global_event_handlers_to_event_target(DeprecatedFlyString const&) override { return *this; }
 
     // ^HTML::WindowEventHandlers
     virtual DOM::EventTarget& window_event_handlers_to_event_target() override { return *this; }
diff --git a/Userland/Libraries/LibWeb/HTML/Worker.cpp b/Userland/Libraries/LibWeb/HTML/Worker.cpp
index 846fb1fca3f..3aac30ea98f 100644
--- a/Userland/Libraries/LibWeb/HTML/Worker.cpp
+++ b/Userland/Libraries/LibWeb/HTML/Worker.cpp
@@ -17,7 +17,7 @@
 namespace Web::HTML {
 
 // https://html.spec.whatwg.org/multipage/workers.html#dedicated-workers-and-the-worker-interface
-Worker::Worker(FlyString const& script_url, WorkerOptions const options, DOM::Document& document)
+Worker::Worker(DeprecatedFlyString const& script_url, WorkerOptions const options, DOM::Document& document)
     : DOM::EventTarget(document.realm())
     , m_script_url(script_url)
     , m_options(options)
@@ -40,7 +40,7 @@ void Worker::visit_edges(Cell::Visitor& visitor)
 }
 
 // https://html.spec.whatwg.org/multipage/workers.html#dom-worker
-WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> Worker::create(FlyString const& script_url, WorkerOptions const options, DOM::Document& document)
+WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> Worker::create(DeprecatedFlyString const& script_url, WorkerOptions const options, DOM::Document& document)
 {
     dbgln_if(WEB_WORKER_DEBUG, "WebWorker: Creating worker with script_url = {}", script_url);
 
diff --git a/Userland/Libraries/LibWeb/HTML/Worker.h b/Userland/Libraries/LibWeb/HTML/Worker.h
index 823a46bc1dd..303ce771539 100644
--- a/Userland/Libraries/LibWeb/HTML/Worker.h
+++ b/Userland/Libraries/LibWeb/HTML/Worker.h
@@ -36,8 +36,8 @@ class Worker : public DOM::EventTarget {
     WEB_PLATFORM_OBJECT(Worker, DOM::EventTarget);
 
 public:
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> create(FlyString const& script_url, WorkerOptions const options, DOM::Document& document);
-    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> construct_impl(JS::Realm& realm, FlyString const& script_url, WorkerOptions const options)
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> create(DeprecatedFlyString const& script_url, WorkerOptions const options, DOM::Document& document);
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<Worker>> construct_impl(JS::Realm& realm, DeprecatedFlyString const& script_url, WorkerOptions const options)
     {
         auto& window = verify_cast<HTML::Window>(realm.global_object());
         return Worker::create(script_url, options, window.associated_document());
@@ -60,7 +60,7 @@ public:
 #undef __ENUMERATE
 
 protected:
-    Worker(FlyString const&, const WorkerOptions, DOM::Document&);
+    Worker(DeprecatedFlyString const&, const WorkerOptions, DOM::Document&);
 
 private:
     static HTML::EventLoop& get_vm_event_loop(JS::VM& target_vm)
@@ -70,7 +70,7 @@ private:
 
     virtual void visit_edges(Cell::Visitor&) override;
 
-    FlyString m_script_url;
+    DeprecatedFlyString m_script_url;
     WorkerOptions m_options;
 
     JS::GCPtr<DOM::Document> m_document;
diff --git a/Userland/Libraries/LibWeb/Namespace.cpp b/Userland/Libraries/LibWeb/Namespace.cpp
index 696a53e9592..eb05860f045 100644
--- a/Userland/Libraries/LibWeb/Namespace.cpp
+++ b/Userland/Libraries/LibWeb/Namespace.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::Namespace {
 
-#define __ENUMERATE_NAMESPACE(name, namespace_) FlyString name;
+#define __ENUMERATE_NAMESPACE(name, namespace_) DeprecatedFlyString name;
 ENUMERATE_NAMESPACES
 #undef __ENUMERATE_NAMESPACE
 
diff --git a/Userland/Libraries/LibWeb/Namespace.h b/Userland/Libraries/LibWeb/Namespace.h
index 17eb9f6bb20..330663dfbf9 100644
--- a/Userland/Libraries/LibWeb/Namespace.h
+++ b/Userland/Libraries/LibWeb/Namespace.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::Namespace {
 
@@ -18,7 +18,7 @@ namespace Web::Namespace {
     __ENUMERATE_NAMESPACE(XML, "http://www.w3.org/XML/1998/namespace")  \
     __ENUMERATE_NAMESPACE(XMLNS, "http://www.w3.org/2000/xmlns/")
 
-#define __ENUMERATE_NAMESPACE(name, namespace_) extern FlyString name;
+#define __ENUMERATE_NAMESPACE(name, namespace_) extern DeprecatedFlyString name;
 ENUMERATE_NAMESPACES
 #undef __ENUMERATE_NAMESPACE
 
diff --git a/Userland/Libraries/LibWeb/Page/EventHandler.cpp b/Userland/Libraries/LibWeb/Page/EventHandler.cpp
index db3e89aa4c3..e196773ed01 100644
--- a/Userland/Libraries/LibWeb/Page/EventHandler.cpp
+++ b/Userland/Libraries/LibWeb/Page/EventHandler.cpp
@@ -661,7 +661,7 @@ constexpr bool should_ignore_keydown_event(u32 code_point)
     return code_point == 0 || code_point == 27;
 }
 
-bool EventHandler::fire_keyboard_event(FlyString const& event_name, HTML::BrowsingContext& browsing_context, KeyCode key, unsigned int modifiers, u32 code_point)
+bool EventHandler::fire_keyboard_event(DeprecatedFlyString const& event_name, HTML::BrowsingContext& browsing_context, KeyCode key, unsigned int modifiers, u32 code_point)
 {
     JS::NonnullGCPtr<DOM::Document> document = *browsing_context.active_document();
     if (!document)
diff --git a/Userland/Libraries/LibWeb/Page/EventHandler.h b/Userland/Libraries/LibWeb/Page/EventHandler.h
index 394cb493cfa..eab3fe08f62 100644
--- a/Userland/Libraries/LibWeb/Page/EventHandler.h
+++ b/Userland/Libraries/LibWeb/Page/EventHandler.h
@@ -40,7 +40,7 @@ private:
     bool focus_next_element();
     bool focus_previous_element();
 
-    bool fire_keyboard_event(FlyString const& event_name, HTML::BrowsingContext& browsing_context, KeyCode key, unsigned modifiers, u32 code_point);
+    bool fire_keyboard_event(DeprecatedFlyString const& event_name, HTML::BrowsingContext& browsing_context, KeyCode key, unsigned modifiers, u32 code_point);
     CSSPixelPoint compute_mouse_event_client_offset(CSSPixelPoint event_page_position) const;
     CSSPixelPoint compute_mouse_event_page_offset(CSSPixelPoint event_client_offset) const;
 
diff --git a/Userland/Libraries/LibWeb/SVG/AttributeNames.cpp b/Userland/Libraries/LibWeb/SVG/AttributeNames.cpp
index f8953aa8228..b24c69a2d86 100644
--- a/Userland/Libraries/LibWeb/SVG/AttributeNames.cpp
+++ b/Userland/Libraries/LibWeb/SVG/AttributeNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::SVG::AttributeNames {
 
-#define __ENUMERATE_SVG_ATTRIBUTE(name) FlyString name;
+#define __ENUMERATE_SVG_ATTRIBUTE(name) DeprecatedFlyString name;
 ENUMERATE_SVG_ATTRIBUTES(__ENUMERATE_SVG_ATTRIBUTE)
 #undef __ENUMERATE_SVG_ATTRIBUTE
 
diff --git a/Userland/Libraries/LibWeb/SVG/AttributeNames.h b/Userland/Libraries/LibWeb/SVG/AttributeNames.h
index 8da65cd1efc..29c64e9718b 100644
--- a/Userland/Libraries/LibWeb/SVG/AttributeNames.h
+++ b/Userland/Libraries/LibWeb/SVG/AttributeNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::SVG::AttributeNames {
 
@@ -87,7 +87,7 @@ namespace Web::SVG::AttributeNames {
     E(yChannelSelector)             \
     E(zoomAndPan)
 
-#define __ENUMERATE_SVG_ATTRIBUTE(name) extern FlyString name;
+#define __ENUMERATE_SVG_ATTRIBUTE(name) extern DeprecatedFlyString name;
 ENUMERATE_SVG_ATTRIBUTES(__ENUMERATE_SVG_ATTRIBUTE)
 #undef __ENUMERATE_SVG_ATTRIBUTE
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGCircleElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGCircleElement.cpp
index 846525b722c..886f8f23207 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGCircleElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGCircleElement.cpp
@@ -17,7 +17,7 @@ SVGCircleElement::SVGCircleElement(DOM::Document& document, DOM::QualifiedName q
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGCircleElement"));
 }
 
-void SVGCircleElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGCircleElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGCircleElement.h b/Userland/Libraries/LibWeb/SVG/SVGCircleElement.h
index 9914dcf7abd..be18108a6d5 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGCircleElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGCircleElement.h
@@ -17,7 +17,7 @@ class SVGCircleElement final : public SVGGeometryElement {
 public:
     virtual ~SVGCircleElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.cpp
index 89ebb21e1f4..ae17c54d03f 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.cpp
@@ -17,7 +17,7 @@ SVGEllipseElement::SVGEllipseElement(DOM::Document& document, DOM::QualifiedName
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGEllipseElement"));
 }
 
-void SVGEllipseElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGEllipseElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.h b/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.h
index e511390f9c4..7473e5f3bce 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGEllipseElement.h
@@ -17,7 +17,7 @@ class SVGEllipseElement final : public SVGGeometryElement {
 public:
     virtual ~SVGEllipseElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGLineElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGLineElement.cpp
index 15fb7d81473..50731211ef8 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGLineElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGLineElement.cpp
@@ -17,7 +17,7 @@ SVGLineElement::SVGLineElement(DOM::Document& document, DOM::QualifiedName quali
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGLineElement"));
 }
 
-void SVGLineElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGLineElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGLineElement.h b/Userland/Libraries/LibWeb/SVG/SVGLineElement.h
index 2c6370c2d31..f5348bd0fd7 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGLineElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGLineElement.h
@@ -17,7 +17,7 @@ class SVGLineElement final : public SVGGeometryElement {
 public:
     virtual ~SVGLineElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp
index 1a856cb2f65..06160679691 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGPathElement.cpp
@@ -90,7 +90,7 @@ SVGPathElement::SVGPathElement(DOM::Document& document, DOM::QualifiedName quali
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGPathElement"));
 }
 
-void SVGPathElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGPathElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPathElement.h b/Userland/Libraries/LibWeb/SVG/SVGPathElement.h
index 0554b44ff6b..7333bd5ad6f 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPathElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGPathElement.h
@@ -19,7 +19,7 @@ class SVGPathElement final : public SVGGeometryElement {
 public:
     virtual ~SVGPathElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.cpp
index 36055827661..e4de0399579 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.cpp
@@ -17,7 +17,7 @@ SVGPolygonElement::SVGPolygonElement(DOM::Document& document, DOM::QualifiedName
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGPolygonElement"));
 }
 
-void SVGPolygonElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGPolygonElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.h b/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.h
index 92d22df9d71..017b57b10a9 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGPolygonElement.h
@@ -16,7 +16,7 @@ class SVGPolygonElement final : public SVGGeometryElement {
 public:
     virtual ~SVGPolygonElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.cpp
index 765a98a0eee..e92d604b97f 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.cpp
@@ -17,7 +17,7 @@ SVGPolylineElement::SVGPolylineElement(DOM::Document& document, DOM::QualifiedNa
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGPolylineElement"));
 }
 
-void SVGPolylineElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGPolylineElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.h b/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.h
index 03e826e0d7d..77015550cb6 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGPolylineElement.h
@@ -16,7 +16,7 @@ class SVGPolylineElement final : public SVGGeometryElement {
 public:
     virtual ~SVGPolylineElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGRectElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGRectElement.cpp
index 95eae3e8aee..1bd6ce469b2 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGRectElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGRectElement.cpp
@@ -19,7 +19,7 @@ SVGRectElement::SVGRectElement(DOM::Document& document, DOM::QualifiedName quali
     set_prototype(&Bindings::cached_web_prototype(realm(), "SVGRectElement"));
 }
 
-void SVGRectElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGRectElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGeometryElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGRectElement.h b/Userland/Libraries/LibWeb/SVG/SVGRectElement.h
index b1429f856ef..6b079a3f05b 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGRectElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGRectElement.h
@@ -17,7 +17,7 @@ class SVGRectElement final : public SVGGeometryElement {
 public:
     virtual ~SVGRectElement() override = default;
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     virtual Gfx::Path& get_path() override;
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGSVGElement.cpp b/Userland/Libraries/LibWeb/SVG/SVGSVGElement.cpp
index cfa061a4d6a..256e3c0be86 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGSVGElement.cpp
+++ b/Userland/Libraries/LibWeb/SVG/SVGSVGElement.cpp
@@ -52,7 +52,7 @@ void SVGSVGElement::apply_presentational_hints(CSS::StyleProperties& style) cons
     }
 }
 
-void SVGSVGElement::parse_attribute(FlyString const& name, DeprecatedString const& value)
+void SVGSVGElement::parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value)
 {
     SVGGraphicsElement::parse_attribute(name, value);
 
diff --git a/Userland/Libraries/LibWeb/SVG/SVGSVGElement.h b/Userland/Libraries/LibWeb/SVG/SVGSVGElement.h
index 3c272ff4719..05fae1059eb 100644
--- a/Userland/Libraries/LibWeb/SVG/SVGSVGElement.h
+++ b/Userland/Libraries/LibWeb/SVG/SVGSVGElement.h
@@ -30,7 +30,7 @@ private:
 
     virtual bool is_svg_svg_element() const override { return true; }
 
-    virtual void parse_attribute(FlyString const& name, DeprecatedString const& value) override;
+    virtual void parse_attribute(DeprecatedFlyString const& name, DeprecatedString const& value) override;
 
     Optional<ViewBox> m_view_box;
 };
diff --git a/Userland/Libraries/LibWeb/SVG/TagNames.cpp b/Userland/Libraries/LibWeb/SVG/TagNames.cpp
index 26ff93d67ff..fe6b698a324 100644
--- a/Userland/Libraries/LibWeb/SVG/TagNames.cpp
+++ b/Userland/Libraries/LibWeb/SVG/TagNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::SVG::TagNames {
 
-#define __ENUMERATE_SVG_TAG(name) FlyString name;
+#define __ENUMERATE_SVG_TAG(name) DeprecatedFlyString name;
 ENUMERATE_SVG_TAGS
 #undef __ENUMERATE_SVG_TAG
 
diff --git a/Userland/Libraries/LibWeb/SVG/TagNames.h b/Userland/Libraries/LibWeb/SVG/TagNames.h
index 41c665c8167..f7794445918 100644
--- a/Userland/Libraries/LibWeb/SVG/TagNames.h
+++ b/Userland/Libraries/LibWeb/SVG/TagNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::SVG::TagNames {
 
@@ -31,7 +31,7 @@ namespace Web::SVG::TagNames {
     __ENUMERATE_SVG_TAG(script)        \
     __ENUMERATE_SVG_TAG(title)
 
-#define __ENUMERATE_SVG_TAG(name) extern FlyString name;
+#define __ENUMERATE_SVG_TAG(name) extern DeprecatedFlyString name;
 ENUMERATE_SVG_TAGS
 #undef __ENUMERATE_SVG_TAG
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/EventNames.cpp b/Userland/Libraries/LibWeb/UIEvents/EventNames.cpp
index 804fad3a042..a84be33b56a 100644
--- a/Userland/Libraries/LibWeb/UIEvents/EventNames.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/EventNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::UIEvents::EventNames {
 
-#define __ENUMERATE_UI_EVENT(name) FlyString name;
+#define __ENUMERATE_UI_EVENT(name) DeprecatedFlyString name;
 ENUMERATE_UI_EVENTS
 #undef __ENUMERATE_UI_EVENT
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/EventNames.h b/Userland/Libraries/LibWeb/UIEvents/EventNames.h
index 14ddd7635ae..22e0892804e 100644
--- a/Userland/Libraries/LibWeb/UIEvents/EventNames.h
+++ b/Userland/Libraries/LibWeb/UIEvents/EventNames.h
@@ -7,7 +7,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::UIEvents::EventNames {
 
@@ -29,7 +29,7 @@ namespace Web::UIEvents::EventNames {
     __ENUMERATE_UI_EVENT(resize)     \
     __ENUMERATE_UI_EVENT(wheel)
 
-#define __ENUMERATE_UI_EVENT(name) extern FlyString name;
+#define __ENUMERATE_UI_EVENT(name) extern DeprecatedFlyString name;
 ENUMERATE_UI_EVENTS
 #undef __ENUMERATE_UI_EVENT
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/FocusEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/FocusEvent.cpp
index 4fc2aeefa9c..30c1deeb508 100644
--- a/Userland/Libraries/LibWeb/UIEvents/FocusEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/FocusEvent.cpp
@@ -9,12 +9,12 @@
 
 namespace Web::UIEvents {
 
-FocusEvent* FocusEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, FocusEventInit const& event_init)
+FocusEvent* FocusEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, FocusEventInit const& event_init)
 {
     return realm.heap().allocate<FocusEvent>(realm, realm, event_name, event_init);
 }
 
-FocusEvent::FocusEvent(JS::Realm& realm, FlyString const& event_name, FocusEventInit const& event_init)
+FocusEvent::FocusEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, FocusEventInit const& event_init)
     : UIEvent(realm, event_name)
 {
     set_prototype(&Bindings::cached_web_prototype(realm, "FocusEvent"));
diff --git a/Userland/Libraries/LibWeb/UIEvents/FocusEvent.h b/Userland/Libraries/LibWeb/UIEvents/FocusEvent.h
index 1df41baecbc..255fba7c807 100644
--- a/Userland/Libraries/LibWeb/UIEvents/FocusEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/FocusEvent.h
@@ -18,12 +18,12 @@ class FocusEvent final : public UIEvent {
     WEB_PLATFORM_OBJECT(FocusEvent, UIEvent);
 
 public:
-    static FocusEvent* construct_impl(JS::Realm&, FlyString const& event_name, FocusEventInit const& event_init);
+    static FocusEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, FocusEventInit const& event_init);
 
     virtual ~FocusEvent() override;
 
 private:
-    FocusEvent(JS::Realm&, FlyString const& event_name, FocusEventInit const&);
+    FocusEvent(JS::Realm&, DeprecatedFlyString const& event_name, FocusEventInit const&);
 };
 
 }
diff --git a/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.cpp
index 997dea18e80..32df18d3975 100644
--- a/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.cpp
@@ -66,7 +66,7 @@ static unsigned long determine_key_code(KeyCode platform_key, u32 code_point)
     return platform_key;
 }
 
-KeyboardEvent* KeyboardEvent::create_from_platform_event(JS::Realm& realm, FlyString const& event_name, KeyCode platform_key, unsigned modifiers, u32 code_point)
+KeyboardEvent* KeyboardEvent::create_from_platform_event(JS::Realm& realm, DeprecatedFlyString const& event_name, KeyCode platform_key, unsigned modifiers, u32 code_point)
 {
     // FIXME: Figure out what these should actually contain.
     DeprecatedString event_key = key_code_to_string(platform_key);
@@ -104,17 +104,17 @@ bool KeyboardEvent::get_modifier_state(DeprecatedString const& key_arg)
     return false;
 }
 
-KeyboardEvent* KeyboardEvent::create(JS::Realm& realm, FlyString const& event_name, KeyboardEventInit const& event_init)
+KeyboardEvent* KeyboardEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init)
 {
     return realm.heap().allocate<KeyboardEvent>(realm, realm, event_name, event_init);
 }
 
-KeyboardEvent* KeyboardEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, KeyboardEventInit const& event_init)
+KeyboardEvent* KeyboardEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-KeyboardEvent::KeyboardEvent(JS::Realm& realm, FlyString const& event_name, KeyboardEventInit const& event_init)
+KeyboardEvent::KeyboardEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init)
     : UIEvent(realm, event_name, event_init)
     , m_key(event_init.key)
     , m_code(event_init.code)
diff --git a/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.h b/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.h
index 495a6ade3f6..c63cd7e192d 100644
--- a/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/KeyboardEvent.h
@@ -28,9 +28,9 @@ class KeyboardEvent final : public UIEvent {
     WEB_PLATFORM_OBJECT(KeyboardEvent, UIEvent);
 
 public:
-    static KeyboardEvent* create(JS::Realm&, FlyString const& event_name, KeyboardEventInit const& event_init = {});
-    static KeyboardEvent* construct_impl(JS::Realm&, FlyString const& event_name, KeyboardEventInit const& event_init);
-    static KeyboardEvent* create_from_platform_event(JS::Realm&, FlyString const& event_name, KeyCode, unsigned modifiers, u32 code_point);
+    static KeyboardEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init = {});
+    static KeyboardEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init);
+    static KeyboardEvent* create_from_platform_event(JS::Realm&, DeprecatedFlyString const& event_name, KeyCode, unsigned modifiers, u32 code_point);
 
     virtual ~KeyboardEvent() override;
 
@@ -54,7 +54,7 @@ public:
     virtual u32 which() const override { return m_key_code; }
 
 private:
-    KeyboardEvent(JS::Realm&, FlyString const& event_name, KeyboardEventInit const& event_init);
+    KeyboardEvent(JS::Realm&, DeprecatedFlyString const& event_name, KeyboardEventInit const& event_init);
 
     DeprecatedString m_key;
     DeprecatedString m_code;
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
index 2e5c19f8f42..d528c8dd68e 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.cpp
@@ -13,7 +13,7 @@
 
 namespace Web::UIEvents {
 
-MouseEvent::MouseEvent(JS::Realm& realm, FlyString const& event_name, MouseEventInit const& event_init)
+MouseEvent::MouseEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, MouseEventInit const& event_init)
     : UIEvent(realm, event_name, event_init)
     , m_offset_x(event_init.offset_x)
     , m_offset_y(event_init.offset_y)
@@ -49,12 +49,12 @@ static i16 determine_button(unsigned mouse_button)
     }
 }
 
-MouseEvent* MouseEvent::create(JS::Realm& realm, FlyString const& event_name, MouseEventInit const& event_init)
+MouseEvent* MouseEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, MouseEventInit const& event_init)
 {
     return realm.heap().allocate<MouseEvent>(realm, realm, event_name, event_init);
 }
 
-MouseEvent* MouseEvent::create_from_platform_event(JS::Realm& realm, FlyString const& event_name, CSSPixelPoint offset, CSSPixelPoint client_offset, CSSPixelPoint page_offset, unsigned buttons, unsigned mouse_button)
+MouseEvent* MouseEvent::create_from_platform_event(JS::Realm& realm, DeprecatedFlyString const& event_name, CSSPixelPoint offset, CSSPixelPoint client_offset, CSSPixelPoint page_offset, unsigned buttons, unsigned mouse_button)
 {
     MouseEventInit event_init {};
     event_init.offset_x = static_cast<double>(offset.x().value());
diff --git a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
index c337bc84dfd..7cbce9c9539 100644
--- a/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/MouseEvent.h
@@ -29,8 +29,8 @@ class MouseEvent : public UIEvent {
     WEB_PLATFORM_OBJECT(MouseEvent, UIEvent);
 
 public:
-    static MouseEvent* create(JS::Realm&, FlyString const& event_name, MouseEventInit const& event_init = {});
-    static MouseEvent* create_from_platform_event(JS::Realm&, FlyString const& event_name, CSSPixelPoint offset, CSSPixelPoint client_offset, CSSPixelPoint page_offset, unsigned buttons, unsigned mouse_button = 1);
+    static MouseEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, MouseEventInit const& event_init = {});
+    static MouseEvent* create_from_platform_event(JS::Realm&, DeprecatedFlyString const& event_name, CSSPixelPoint offset, CSSPixelPoint client_offset, CSSPixelPoint page_offset, unsigned buttons, unsigned mouse_button = 1);
 
     virtual ~MouseEvent() override;
 
@@ -56,7 +56,7 @@ public:
     virtual u32 which() const override { return m_button + 1; }
 
 protected:
-    MouseEvent(JS::Realm&, FlyString const& event_name, MouseEventInit const& event_init);
+    MouseEvent(JS::Realm&, DeprecatedFlyString const& event_name, MouseEventInit const& event_init);
 
 private:
     void set_event_characteristics();
diff --git a/Userland/Libraries/LibWeb/UIEvents/UIEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/UIEvent.cpp
index e7488a3b5bf..f97f07fb165 100644
--- a/Userland/Libraries/LibWeb/UIEvents/UIEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/UIEvent.cpp
@@ -9,23 +9,23 @@
 
 namespace Web::UIEvents {
 
-UIEvent* UIEvent::create(JS::Realm& realm, FlyString const& event_name)
+UIEvent* UIEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name)
 {
     return realm.heap().allocate<UIEvent>(realm, realm, event_name);
 }
 
-UIEvent* UIEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, UIEventInit const& event_init)
+UIEvent* UIEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, UIEventInit const& event_init)
 {
     return realm.heap().allocate<UIEvent>(realm, realm, event_name, event_init);
 }
 
-UIEvent::UIEvent(JS::Realm& realm, FlyString const& event_name)
+UIEvent::UIEvent(JS::Realm& realm, DeprecatedFlyString const& event_name)
     : Event(realm, event_name)
 {
     set_prototype(&Bindings::cached_web_prototype(realm, "UIEvent"));
 }
 
-UIEvent::UIEvent(JS::Realm& realm, FlyString const& event_name, UIEventInit const& event_init)
+UIEvent::UIEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, UIEventInit const& event_init)
     : Event(realm, event_name, event_init)
     , m_view(event_init.view)
     , m_detail(event_init.detail)
diff --git a/Userland/Libraries/LibWeb/UIEvents/UIEvent.h b/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
index 3bb70e49afe..874a9d9399e 100644
--- a/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/UIEvent.h
@@ -21,8 +21,8 @@ class UIEvent : public DOM::Event {
     WEB_PLATFORM_OBJECT(UIEvent, DOM::Event);
 
 public:
-    static UIEvent* create(JS::Realm&, FlyString const& type);
-    static UIEvent* construct_impl(JS::Realm&, FlyString const& event_name, UIEventInit const& event_init);
+    static UIEvent* create(JS::Realm&, DeprecatedFlyString const& type);
+    static UIEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, UIEventInit const& event_init);
 
     virtual ~UIEvent() override;
 
@@ -38,8 +38,8 @@ public:
     }
 
 protected:
-    UIEvent(JS::Realm&, FlyString const& event_name);
-    UIEvent(JS::Realm&, FlyString const& event_name, UIEventInit const& event_init);
+    UIEvent(JS::Realm&, DeprecatedFlyString const& event_name);
+    UIEvent(JS::Realm&, DeprecatedFlyString const& event_name, UIEventInit const& event_init);
 
     virtual void visit_edges(Cell::Visitor&) override;
 
diff --git a/Userland/Libraries/LibWeb/UIEvents/WheelEvent.cpp b/Userland/Libraries/LibWeb/UIEvents/WheelEvent.cpp
index c6584f1966d..d8d92f503b1 100644
--- a/Userland/Libraries/LibWeb/UIEvents/WheelEvent.cpp
+++ b/Userland/Libraries/LibWeb/UIEvents/WheelEvent.cpp
@@ -11,7 +11,7 @@
 
 namespace Web::UIEvents {
 
-WheelEvent::WheelEvent(JS::Realm& realm, FlyString const& event_name, WheelEventInit const& event_init)
+WheelEvent::WheelEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, WheelEventInit const& event_init)
     : MouseEvent(realm, event_name, event_init)
     , m_delta_x(event_init.delta_x)
     , m_delta_y(event_init.delta_y)
@@ -23,12 +23,12 @@ WheelEvent::WheelEvent(JS::Realm& realm, FlyString const& event_name, WheelEvent
 
 WheelEvent::~WheelEvent() = default;
 
-WheelEvent* WheelEvent::create(JS::Realm& realm, FlyString const& event_name, WheelEventInit const& event_init)
+WheelEvent* WheelEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, WheelEventInit const& event_init)
 {
     return realm.heap().allocate<WheelEvent>(realm, realm, event_name, event_init);
 }
 
-WheelEvent* WheelEvent::create_from_platform_event(JS::Realm& realm, FlyString const& event_name, CSSPixels offset_x, CSSPixels offset_y, CSSPixels client_x, CSSPixels client_y, double delta_x, double delta_y, unsigned buttons, unsigned button)
+WheelEvent* WheelEvent::create_from_platform_event(JS::Realm& realm, DeprecatedFlyString const& event_name, CSSPixels offset_x, CSSPixels offset_y, CSSPixels client_x, CSSPixels client_y, double delta_x, double delta_y, unsigned buttons, unsigned button)
 {
     WheelEventInit event_init {};
     event_init.offset_x = static_cast<double>(offset_x.value());
diff --git a/Userland/Libraries/LibWeb/UIEvents/WheelEvent.h b/Userland/Libraries/LibWeb/UIEvents/WheelEvent.h
index 47ab277af58..f3f65eae675 100644
--- a/Userland/Libraries/LibWeb/UIEvents/WheelEvent.h
+++ b/Userland/Libraries/LibWeb/UIEvents/WheelEvent.h
@@ -29,8 +29,8 @@ class WheelEvent final : public MouseEvent {
     WEB_PLATFORM_OBJECT(WheelEvent, MouseEvent);
 
 public:
-    static WheelEvent* create(JS::Realm&, FlyString const& event_name, WheelEventInit const& event_init = {});
-    static WheelEvent* create_from_platform_event(JS::Realm&, FlyString const& event_name, CSSPixels offset_x, CSSPixels offset_y, CSSPixels client_x, CSSPixels client_y, double delta_x, double delta_y, unsigned buttons, unsigned button);
+    static WheelEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, WheelEventInit const& event_init = {});
+    static WheelEvent* create_from_platform_event(JS::Realm&, DeprecatedFlyString const& event_name, CSSPixels offset_x, CSSPixels offset_y, CSSPixels client_x, CSSPixels client_y, double delta_x, double delta_y, unsigned buttons, unsigned button);
 
     virtual ~WheelEvent() override;
 
@@ -40,7 +40,7 @@ public:
     unsigned long delta_mode() const { return to_underlying(m_delta_mode); }
 
 private:
-    WheelEvent(JS::Realm&, FlyString const& event_name, WheelEventInit const& event_init);
+    WheelEvent(JS::Realm&, DeprecatedFlyString const& event_name, WheelEventInit const& event_init);
 
     void set_event_characteristics();
 
diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.cpp b/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.cpp
index 343a8c2a0be..983899ad8b6 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.cpp
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::WebGL {
 
-WebGLContextEvent* WebGLContextEvent::create(JS::Realm& realm, FlyString const& event_name, WebGLContextEventInit const& event_init)
+WebGLContextEvent* WebGLContextEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, WebGLContextEventInit const& event_init)
 {
     return realm.heap().allocate<WebGLContextEvent>(realm, realm, event_name, event_init);
 }
 
-WebGLContextEvent* WebGLContextEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, WebGLContextEventInit const& event_init)
+WebGLContextEvent* WebGLContextEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, WebGLContextEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-WebGLContextEvent::WebGLContextEvent(JS::Realm& realm, FlyString const& type, WebGLContextEventInit const& event_init)
+WebGLContextEvent::WebGLContextEvent(JS::Realm& realm, DeprecatedFlyString const& type, WebGLContextEventInit const& event_init)
     : DOM::Event(realm, type, event_init)
     , m_status_message(event_init.status_message)
 {
diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.h b/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.h
index f159850a1be..23cd69d0fdc 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.h
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLContextEvent.h
@@ -19,15 +19,15 @@ class WebGLContextEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(WebGLContextEvent, DOM::Event);
 
 public:
-    static WebGLContextEvent* create(JS::Realm&, FlyString const& type, WebGLContextEventInit const& event_init);
-    static WebGLContextEvent* construct_impl(JS::Realm&, FlyString const& type, WebGLContextEventInit const& event_init);
+    static WebGLContextEvent* create(JS::Realm&, DeprecatedFlyString const& type, WebGLContextEventInit const& event_init);
+    static WebGLContextEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& type, WebGLContextEventInit const& event_init);
 
     virtual ~WebGLContextEvent() override;
 
     DeprecatedString const& status_message() const { return m_status_message; }
 
 private:
-    WebGLContextEvent(JS::Realm&, FlyString const& type, WebGLContextEventInit const& event_init);
+    WebGLContextEvent(JS::Realm&, DeprecatedFlyString const& type, WebGLContextEventInit const& event_init);
 
     DeprecatedString m_status_message { DeprecatedString::empty() };
 };
diff --git a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp
index e540f002f05..54557345b81 100644
--- a/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp
+++ b/Userland/Libraries/LibWeb/WebGL/WebGLRenderingContext.cpp
@@ -13,7 +13,7 @@
 namespace Web::WebGL {
 
 // https://www.khronos.org/registry/webgl/specs/latest/1.0/#fire-a-webgl-context-event
-static void fire_webgl_context_event(HTML::HTMLCanvasElement& canvas_element, FlyString const& type)
+static void fire_webgl_context_event(HTML::HTMLCanvasElement& canvas_element, DeprecatedFlyString const& type)
 {
     // To fire a WebGL context event named e means that an event using the WebGLContextEvent interface, with its type attribute [DOM4] initialized to e, its cancelable attribute initialized to true, and its isTrusted attribute [DOM4] initialized to true, is to be dispatched at the given object.
     // FIXME: Consider setting a status message.
diff --git a/Userland/Libraries/LibWeb/WebIDL/DOMException.cpp b/Userland/Libraries/LibWeb/WebIDL/DOMException.cpp
index 723eeef2045..49709af9a59 100644
--- a/Userland/Libraries/LibWeb/WebIDL/DOMException.cpp
+++ b/Userland/Libraries/LibWeb/WebIDL/DOMException.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::WebIDL {
 
-JS::NonnullGCPtr<DOMException> DOMException::create(JS::Realm& realm, FlyString const& name, FlyString const& message)
+JS::NonnullGCPtr<DOMException> DOMException::create(JS::Realm& realm, DeprecatedFlyString const& name, DeprecatedFlyString const& message)
 {
     return realm.heap().allocate<DOMException>(realm, realm, name, message);
 }
 
-JS::NonnullGCPtr<DOMException> DOMException::construct_impl(JS::Realm& realm, FlyString const& message, FlyString const& name)
+JS::NonnullGCPtr<DOMException> DOMException::construct_impl(JS::Realm& realm, DeprecatedFlyString const& message, DeprecatedFlyString const& name)
 {
     return realm.heap().allocate<DOMException>(realm, realm, name, message);
 }
 
-DOMException::DOMException(JS::Realm& realm, FlyString const& name, FlyString const& message)
+DOMException::DOMException(JS::Realm& realm, DeprecatedFlyString const& name, DeprecatedFlyString const& message)
     : PlatformObject(realm)
     , m_name(name)
     , m_message(message)
diff --git a/Userland/Libraries/LibWeb/WebIDL/DOMException.h b/Userland/Libraries/LibWeb/WebIDL/DOMException.h
index 17bd1c4bba0..38b86efc24e 100644
--- a/Userland/Libraries/LibWeb/WebIDL/DOMException.h
+++ b/Userland/Libraries/LibWeb/WebIDL/DOMException.h
@@ -6,8 +6,8 @@
 
 #pragma once
 
+#include <AK/DeprecatedFlyString.h>
 #include <AK/Diagnostics.h>
-#include <AK/FlyString.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibWeb/Bindings/PlatformObject.h>
 #include <LibWeb/HTML/Scripting/Environments.h>
@@ -79,7 +79,7 @@ namespace Web::WebIDL {
     __ENUMERATE(OperationError)                      \
     __ENUMERATE(NotAllowedError)
 
-static u16 get_legacy_code_for_name(FlyString const& name)
+static u16 get_legacy_code_for_name(DeprecatedFlyString const& name)
 {
 #define __ENUMERATE(ErrorName, code) \
     if (name == #ErrorName)          \
@@ -94,33 +94,33 @@ class DOMException final : public Bindings::PlatformObject {
     WEB_PLATFORM_OBJECT(DOMException, Bindings::PlatformObject);
 
 public:
-    static JS::NonnullGCPtr<DOMException> create(JS::Realm& realm, FlyString const& name, FlyString const& message);
+    static JS::NonnullGCPtr<DOMException> create(JS::Realm& realm, DeprecatedFlyString const& name, DeprecatedFlyString const& message);
 
     // JS constructor has message first, name second
     // FIXME: This is a completely pointless footgun, let's use the same order for both factories.
-    static JS::NonnullGCPtr<DOMException> construct_impl(JS::Realm& realm, FlyString const& message, FlyString const& name);
+    static JS::NonnullGCPtr<DOMException> construct_impl(JS::Realm& realm, DeprecatedFlyString const& message, DeprecatedFlyString const& name);
 
     virtual ~DOMException() override;
 
-    FlyString const& name() const { return m_name; }
-    FlyString const& message() const { return m_message; }
+    DeprecatedFlyString const& name() const { return m_name; }
+    DeprecatedFlyString const& message() const { return m_message; }
     u16 code() const { return get_legacy_code_for_name(m_name); }
 
 protected:
-    DOMException(JS::Realm&, FlyString const& name, FlyString const& message);
+    DOMException(JS::Realm&, DeprecatedFlyString const& name, DeprecatedFlyString const& message);
 
 private:
-    FlyString m_name;
-    FlyString m_message;
+    DeprecatedFlyString m_name;
+    DeprecatedFlyString m_message;
 };
 
-#define __ENUMERATE(ErrorName)                                                                   \
-    class ErrorName final {                                                                      \
-    public:                                                                                      \
-        static JS::NonnullGCPtr<DOMException> create(JS::Realm& realm, FlyString const& message) \
-        {                                                                                        \
-            return DOMException::create(realm, #ErrorName, message);                             \
-        }                                                                                        \
+#define __ENUMERATE(ErrorName)                                                                             \
+    class ErrorName final {                                                                                \
+    public:                                                                                                \
+        static JS::NonnullGCPtr<DOMException> create(JS::Realm& realm, DeprecatedFlyString const& message) \
+        {                                                                                                  \
+            return DOMException::create(realm, #ErrorName, message);                                       \
+        }                                                                                                  \
     };
 ENUMERATE_DOM_EXCEPTION_ERROR_NAMES
 #undef __ENUMERATE
diff --git a/Userland/Libraries/LibWeb/XHR/EventNames.cpp b/Userland/Libraries/LibWeb/XHR/EventNames.cpp
index 8f79bd5e2c7..b3848d0b9e5 100644
--- a/Userland/Libraries/LibWeb/XHR/EventNames.cpp
+++ b/Userland/Libraries/LibWeb/XHR/EventNames.cpp
@@ -8,7 +8,7 @@
 
 namespace Web::XHR::EventNames {
 
-#define __ENUMERATE_XHR_EVENT(name) FlyString name;
+#define __ENUMERATE_XHR_EVENT(name) DeprecatedFlyString name;
 ENUMERATE_XHR_EVENTS
 #undef __ENUMERATE_XHR_EVENT
 
diff --git a/Userland/Libraries/LibWeb/XHR/EventNames.h b/Userland/Libraries/LibWeb/XHR/EventNames.h
index c1e222b61fa..9cf36a61027 100644
--- a/Userland/Libraries/LibWeb/XHR/EventNames.h
+++ b/Userland/Libraries/LibWeb/XHR/EventNames.h
@@ -6,7 +6,7 @@
 
 #pragma once
 
-#include <AK/FlyString.h>
+#include <AK/DeprecatedFlyString.h>
 
 namespace Web::XHR::EventNames {
 
@@ -20,7 +20,7 @@ namespace Web::XHR::EventNames {
     __ENUMERATE_XHR_EVENT(timeout)          \
     __ENUMERATE_XHR_EVENT(loadend)
 
-#define __ENUMERATE_XHR_EVENT(name) extern FlyString name;
+#define __ENUMERATE_XHR_EVENT(name) extern DeprecatedFlyString name;
 ENUMERATE_XHR_EVENTS
 #undef __ENUMERATE_XHR_EVENT
 
diff --git a/Userland/Libraries/LibWeb/XHR/ProgressEvent.cpp b/Userland/Libraries/LibWeb/XHR/ProgressEvent.cpp
index 10bba97a879..d26f53cce2a 100644
--- a/Userland/Libraries/LibWeb/XHR/ProgressEvent.cpp
+++ b/Userland/Libraries/LibWeb/XHR/ProgressEvent.cpp
@@ -9,17 +9,17 @@
 
 namespace Web::XHR {
 
-ProgressEvent* ProgressEvent::create(JS::Realm& realm, FlyString const& event_name, ProgressEventInit const& event_init)
+ProgressEvent* ProgressEvent::create(JS::Realm& realm, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init)
 {
     return realm.heap().allocate<ProgressEvent>(realm, realm, event_name, event_init);
 }
 
-ProgressEvent* ProgressEvent::construct_impl(JS::Realm& realm, FlyString const& event_name, ProgressEventInit const& event_init)
+ProgressEvent* ProgressEvent::construct_impl(JS::Realm& realm, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init)
 {
     return create(realm, event_name, event_init);
 }
 
-ProgressEvent::ProgressEvent(JS::Realm& realm, FlyString const& event_name, ProgressEventInit const& event_init)
+ProgressEvent::ProgressEvent(JS::Realm& realm, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init)
     : Event(realm, event_name, event_init)
     , m_length_computable(event_init.length_computable)
     , m_loaded(event_init.loaded)
diff --git a/Userland/Libraries/LibWeb/XHR/ProgressEvent.h b/Userland/Libraries/LibWeb/XHR/ProgressEvent.h
index e5d633920e1..3ef9daf643d 100644
--- a/Userland/Libraries/LibWeb/XHR/ProgressEvent.h
+++ b/Userland/Libraries/LibWeb/XHR/ProgressEvent.h
@@ -23,8 +23,8 @@ class ProgressEvent final : public DOM::Event {
     WEB_PLATFORM_OBJECT(ProgressEvent, DOM::Event);
 
 public:
-    static ProgressEvent* create(JS::Realm&, FlyString const& event_name, ProgressEventInit const& event_init);
-    static ProgressEvent* construct_impl(JS::Realm&, FlyString const& event_name, ProgressEventInit const& event_init);
+    static ProgressEvent* create(JS::Realm&, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init);
+    static ProgressEvent* construct_impl(JS::Realm&, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init);
 
     virtual ~ProgressEvent() override;
 
@@ -33,7 +33,7 @@ public:
     u64 total() const { return m_total; }
 
 private:
-    ProgressEvent(JS::Realm&, FlyString const& event_name, ProgressEventInit const& event_init);
+    ProgressEvent(JS::Realm&, DeprecatedFlyString const& event_name, ProgressEventInit const& event_init);
 
     bool m_length_computable { false };
     u64 m_loaded { 0 };
diff --git a/Userland/Libraries/LibWeb/XML/XMLDocumentBuilder.cpp b/Userland/Libraries/LibWeb/XML/XMLDocumentBuilder.cpp
index 75ddd24b1b7..a58eb817672 100644
--- a/Userland/Libraries/LibWeb/XML/XMLDocumentBuilder.cpp
+++ b/Userland/Libraries/LibWeb/XML/XMLDocumentBuilder.cpp
@@ -14,7 +14,7 @@ inline namespace {
 extern char const* s_xhtml_unified_dtd;
 }
 
-static FlyString s_html_namespace = "http://www.w3.org/1999/xhtml";
+static DeprecatedFlyString s_html_namespace = "http://www.w3.org/1999/xhtml";
 
 namespace Web {