Change Firefox logo name to Mozilla

Mozilla has announced the end of Firefox accounts, which will all be renamed as Mozilla accounts. "Firefox" title will continue to work by pointing to the file mozilla.svg.

assets/custom-icons/_data/custom-icons.json

@@ -52,7 +52,8 @@
       "hex": "858585"
     },
     {
-      "title": "Firefox"
+      "title": "Firefox",
+      "slug": "mozilla"
     },
     {
       "title": "GitHub",
@@ -97,6 +98,9 @@
     {
       "title": "Microsoft"
     },
+    {
+      "title": "Mozilla"
+    },
     {
       "title": "ngrok",
       "hex": "858585"