The Burning Edge

Speed & memory:

• Fixed: 784591 - Don't leave around decoded image data for display: none images.
• Fixed: 836010 - When startup is determined to be slow, tell users about ways to improve their startup time.
• Fixed: 823147 - Avoid hitting D2D slow path when drawing radial gradients from css.
• Fixed: 821361 - JS: Optimize closures that only run once.
• Fixed: 807853 - JS: Add parallel compilation mode.
• Fixed: 715419 - JS: Specialize Array.prototype.sort when given the comparator is "return arg1 - arg2".
• Fixed: 835417 - DOM: Mark DOM getters as pure when they are.
• Fixed: 239254 - [Linux] Support disk cache on a local path.

For more, read Taras's Snappy blog and Nick's MemShrink blog.

New web technologies:

• Fixed: 820508 - Add support for <main> element.
• Fixed: 508725 - Implement scoped stylesheets.
• Fixed: 440046 - Implement window.crypto.getRandomValues (secure PRNG).
• Fixed: 828261 - Implement window.location.origin.
• Fixed: 792263 - Implement decodeAudioData.
• Fixed: 796463 - Enable WebRTC's PeerConnection by default.

For more, read Firefox 21 for developers.

Security & privacy:

• Fixed: 838557 - Create and use a common interface for ASan/Valgrind memory handling functions.
• Fixed: 821892 - Click-to-play: "Page Info" -> Permissions needs to be aware of plugin permission differentiation.
• Fixed: 774315 - Click-to-play: Add "Hide this plugin" to context menu, to work around broken sites.
• Fixed: 822371 - Mixed content: Improved UI for users who have set security.mixed_content.block_active_content.

Other notable fixes:

• Fixed: 833511 - Add rotation gesture support to image documents.
• Fixed: 765398 - Implement three-state UI for DNT (do not track me, okay to track me, decline to state).
• Fixed: 815640 - Make permission manager aware of "file://" (without dirty hacks).
• Fixed: 726275 - Shift-click on back/forward button doesn't load page.
• Fixed: 712763 - Session restore loads saved windows in reverse order.
• Fixed: 608735 - DOM: XMLHttpRequest's getAllResponseHeaders() returns null if the request is the result of CORS.
• Fixed: 838269 - DOM: Support cross-global |... instanceof DOMInterface|.
• Fixed: 777385 - DOM: Support Paris bindings objects that are either nsISupports or non-cycle-collected as weak map keys.
• Fixed: 818023 - JS: function.caller does not always work.
• Fixed: 786135 - JS: Make parseInt("042") === 42.
• Fixed: 827784 - [Windows] Provide an option to disable favicons on webpage shortcuts.
• Fixed: 837859 - [Windows] Enable Windows Media Foundation support for H.264 AAC, and MP3 playback on Windows 7 and later.
• Fixed: 813488 - [Windows] Enable metro browser build.

All 4385 changes between FIREFOX_AURORA_20_BASE and FIREFOX_AURORA_21_BASE