Web2 Developers

• NEW: Enhanced three-state UI for Do Not Track (DNT).
• NEW: Firefox will suggest how to improve your application startup time if needed.
• NEW: Preliminary implementation of Firefox Health Report (see FAQ).
• CHANGED: Ability to Restore removed thumbnails on New tab Page.
• CHANGED: Add-ons History API removals in Places.
• CHANGED: CSS -moz-user-select:none selection changed to improve compatibility with -webkit-user-select:none (bugs 816298).
• CHANGED: Graphics related performance improvements (bugs 809821).
• CHANGED: Removed E4X support from SpiderMonkey.
• DEVELOPER: Implemented Remote Profiling.
• DEVELOPER: Integrated, Add-on SDK loader and API libraries into Firefox.
• HTML5: Added support for <main> element.
• HTML5: Implemented scoped stylesheets.
• FIXED: Some function keys may not work when pressed (833719).
• FIXED: Browsing and Download history clearing needs unification to avoid confusion on clearing download history
  (847627).

Firefox 21 for Android hasn’t been pushed out yet, but keep checking for app updates over on Google Play. Our coverage of the beta is here, and again, the beta changelog is as follows:

• NEW: Shipping Open Sans and Charis fonts for Web Content.
• NEW: Ability to save media files on long tap.
• CHANGED: Polished UI based on Holo theme.
• CHANGED: CSS -moz-user-select:none selection changed to improve compatibility with -webkit-user-select:none (bugs 816298).
• CHANGED: Graphics related performance improvements (bug 809821).
• CHANGED: Removed E4X support from SpiderMonkey.
• DEVELOPER: Implemented Remote Profiling.
• DEVELOPER: Integrated, Add-on SDK loader and API libraries into Firefox.
• DEVELOPER: DOM/content implementation for <input type=’time’> Associated bugs.
• HTML5: Added support for <main> element.
• HTML5: Implemented scoped stylesheets.
• FIXED: Download Manager page is not updated after clearing private data
  (777639).
• FIXED: In content UI cut off on small screens
  (840593).

We will update you with more information (including the official changelog) when Firefox 21 officially launches. In the meantime, if you’re a Web developer, you may want to check out the Firefox 21 for developers page.