12.0
*NEW
- Firefox is now easier to update with one less prompt (User Account Control)
- Page Source now has line numbers
*Changed
- Line breaks are now supported in the title attribute
- Improvements to "Find in Page" to center search result
- URLs pasted into the download manager window are now automatically downloaded
*Developer
- Support for the text-align-last CSS property has been added
- Experimental support for ECMAScript 6 Map and Set objects has been implemented
*Fixed
- Various security fixes
- Some TinyMCE-based editors failed to load (739141)
- OS X: WebGL performance may be degraded on some hardware (713305) 

11.0
* NEW
- Firefox can now migrate your bookmarks, history, and cookies from Google Chrome
- With Sync enabled, add-ons can now be synchronized across your computers
- The CSS text-size-adjust property is now supported
* HTML5
- The outerHTML property is now supported on HTML elements
- View source syntax highlighting now uses the HTML5 parser
* DEVELOPER
- The Style Editor for CSS editing is now available to web developers
- Web developers can now visualize a web page in 3D using the Page Inspector 3D View
- SPDY protocol support for faster page loads is now testable
- XMLHttpRequest now supports HTML parsing
- Files can now be stored in IndexedDB 

10.0
* NEW
- The forward button is now hidden until you navigate back
- Anti-Aliasing for WebGL is now implemented
- Full Screen APIs allow you to build a web application that runs full screen (see the feature page)
- CSS3 3D-Transforms are now supported
* HTML5
- New <bdi> element for bi-directional text isolation, along with supporting CSS properties
* DEVELOPER
- Inspect tool with content highlighting, includes new CSS Style Inspector
- We've added IndexedDB APIs to more closely match the specification
* FIXED
- Some users may experience a crash when moving bookmarks 

9.0
- Added Type Inference, significantly improving JavaScript performance
- Improved theme integration for Mac OS X Lion
- Added two finger swipe navigation for Mac OS X Lion
- Added support for querying Do Not Track status via JavaScript
- Added support for font-stretch
- Improved support for text-overflow
- Improved standards support for HTML5, MathML, and CSS
- Fixed several stability issues
- Fixed several security issues

8.0
- Add-ons installed by third-party programs are now disabled by default
- Added a one-time add-on selection dialog to manage previously installed add-ons
- Added Twitter to the search bar
- Added a preference to load tabs on demand, improving start-up time when windows are restored
- Improved performance and memory handling when using <audio> and <video> elements
- Added Cross-Origin Resource Sharing (CORS) support for cross-domain textures in WebGL
- Added support for HTML5 context menus
- Added support for insertAdjacentHTML
- Improved CSS hyphen support for many languages
- Improved WebSocket support
- Fixed several stability issues

7.0
- Drastically improved memory handling for certain use cases
- Added a new rendering backend to speed up Canvas operations on Windows systems
- Bookmark and password changes now sync almost instantly when using Firefox Sync
- The 'http://' URL prefix is now hidden by default
- Added support for text-overflow: ellipsis
- Added support for the Web Timing specification
- Enhanced support for MathML
- The WebSocket protocol has been updated from version 7 to version 8
- Added an opt-in system for users to send performance data back to Mozilla to improve future versions of Firefox
- Fixed several stability issues
- Fixed several security issues

6.0
- The address bar now highlights the domain of the website you're visiting
- Streamlined the look of the site identity block
- Added support for the latest draft version of WebSockets with a prefixed API
- Added support for EventSource / server-sent events
- Added support for window.matchMedia
- Added Scratchpad, an interactive JavaScript prototyping environment
- Added a new Web Developer menu item and moved development-related items into it
- Improved usability of the Web Console
- Improved the discoverability of Firefox Sync
- Reduced browser startup time when using Panorama
- Fixed several stability issues
- Fixed several security issues

5.0.1
- Worked around an issue in Mac OS X 10.7 that would cause Firefox to crash
- Worked around an issue caused by Apple's "Java for Mac OS X 10.6 Update 5" where the Java plugin would not be loaded

5.0
- Added support for CSS animations
- The Do-Not-Track header preference has been moved to increase discoverability
- Tuned HTTP idle connection logic for increased performance
- Improved canvas, JavaScript, memory, and networking performance
- Improved standards support for HTML5, XHR, MathML, SMIL, and canvas
- Improved spell checking for some locales
- Improved desktop environment integration for Linux users
- WebGL content can no longer load cross-domain textures
- Background tabs have setTimeout and setInterval clamped to 1000ms to improve -performance
- Fixed several stability issues
- Fixed several security issues

5.0 Beta 2
- Added support for CSS animations
- Added support for switching Firefox development channels
- The Do-Not-Track header preference has been moved to increase discoverability
- Improved canvas, JavaScript, memory, and networking performance
- Improved standards support for HTML5, XHR, MathML, SMIL, and canvas
- Improved spell checking for some locales
- Improved desktop environment integration for Linux users

4.0.1
- Fixed several security issues.
- Fixed several stability issues.

4.0
- Uses JägerMonkey, a new, faster JavaScript engine that is up to six times faster than Firefox 3.6
- Support for the Do Not Track ("DNT") header that allows users to opt-out of behavioural advertising
- Firefox Sync is included by default, allowing you to securely synchronize between multiple computers and mobile devices
- Certain graphics rendering operations are now hardware-accelerated using Direct3D 9 on Windows XP, Direct3D 10 on Windows Vista and 7, and OpenGL on Mac OS (OpenGL on Linux will be supported in the future)
- Direct2D Hardware Acceleration is now on by default for Windows 7 users
- WebGL is enabled on all platforms that have a capable graphics card with updated drivers
- Native support for the HD HTML5 WebM video format, hardware accelerated where available
- Firefox button has a new look for Windows Vista and Windows 7 users
- Tabs are now on top by default on Windows, Mac OS X, and Linux
- You can search for and switch to already open tabs in the Smart Location Bar
- The stop and reload buttons have been merged into a single button on Windows, Mac OS X, and Linux
- The Bookmarks Toolbar has been replaced with a Bookmarks Button by default (you can switch it back if you'd like)
- Crash protection for Windows, Linux, and Mac OS X when there is a crash in the Adobe Flash, Apple Quicktime or Microsoft Silverlight plugins
- You can turn any tab into an "App Tab" by right-clicking on it and selecting "Make into App Tab" from the context menu
- The default homepage design has been refreshed
- Overhaul of the bookmarks and history code, enabling faster bookmarking and startup performance
- Per-compartment garbage collection is now enabled, reducing work done during complex animations
- Additional polish for the Firefox Add-ons Manager
- Improved web typography using OpenType with support for ligatures, kerning and font variants
- Web developers can animate content using CSS Transitions
- Responsiveness and scrolling improvements from the new retained layers layout system
- HTML5 Forms API makes web based forms easier to implement and validate
- Support for the new proposed Audio Data API
- Support for HSTS security protocol allowing sites to insist that they only be loaded over SSL
- A new feature called Panorama gives users a visual overview of all open tabs, allowing them to be sorted and grouped
- An experimental API is included to provide more efficient Javascript animations
- Firefox now supports the HTML5 video "buffered" property
- Changes to how XPCOM components are registered in order to help startup time and process separation
- New Addons Manager and extension management API (UI will be changed before final release)
- Significant API improvements are available for JS-ctypes, a foreign function interface for extensions
- CSS Transitions are partially supported
- Core Animation rendering model for plugins on Mac OS X. Plugins which also support this rendering model can now draw faster and more efficiently
- Web developers can update the URL field without reloading the page using HTML History APIs
- More responsive page rendering using lazy frame construction
- Link history lookup is done asynchronously to provide better responsiveness during pageload
- CSS :visited selectors have been changed to block websites from being able to check a user's browsing history
- New HTML5 parser
- Support for more HTML5 form controls
- Web authors can now get touch events from Firefox users on Windows 7 machines
- A new way of representing values in JavaScript that allows Firefox to execute heavy, numeric code (used for things like graphics and animations) more efficiently

4.0 RC 2
- Blacklisted a few invalid HTTPS certificates
- Updated localizations for 29 locales
- Added Vietnamese localization, bringing the total languages available in Firefox 4 to 83

4.0 RC 1
- General stability, performance, and compatibility improvements.

4.0 Beta 12
- Increased performance while viewing Flash content
- Improved plugin compatibility with hardware acceleration enabled
- Hovering over links now displays the URL at the bottom of the window rather than in the location bar
- General stability, performance, and compatibility improvements

4.0 Beta 11
- Support for the proposed Do Not Track ("DNT") header
- Connection status messages are now shown in a small overlay
- WebGL has been re-enabled on Linux
- The default homepage design has been refreshed
- Firefox no longer switches into offline mode automatically

4.0 Beta 10
- Compatibilty and stability improvements when using Adobe Flash on Mac OS X
- Improvements in memory usage
- Support for a graphics driver blacklist to improve stability

4.0 Beta 9
- Overhaul of the bookmarks and history code, enabling faster bookmarking and startup performance
- Per-compartment garbage collection is now enabled, reducing work done during complex animations

4.0 Beta 8
- The Firefox Sync setup experience has been greatly improved across desktop and mobile devices
- Speed, functionality, and compatibility improvements to WebGL
- Additional polish for the Firefox Add-ons Manager

4.0 Beta 7
- Uses JägerMonkey, a new, faster JavaScript engine
- WebGL is enabled by default on Windows and Mac OS X. WebGL support requires an OpenGL-capable graphics card. Support for other graphics cards on Windows (specifically Intel GPUs) and Linux will be coming in a future beta
- Certain rendering operations are now hardware-accelerated using Direct3D 9 on Windows XP, Direct3D 10 on Windows Vista and 7, and OpenGL on Mac OS X
- Improved web typography using OpenType with support for ligatures, kerning and font variants
- HTML5 Forms API makes web based forms easier to implement and validate

4.0 Beta 6
- Fixed a stability issue affecting Windows users.

4.0 Beta 5
- Support for the new proposed Audio Data API
- Direct2D Hardware Acceleration is now on by default for Windows 7 users
- Firefox button has a new look for Windows Vista and Windows 7 users
- Support for HSTS security protocol allowing sites to insist that they only be loaded over SSL.

4.0 Beta 4
- Firefox Sync is now included by default.
- A new feature gives users a visual overview of all open tabs, allowing them to be sorted and grouped.
- An experimental API is included to provide more efficient Javascript animations.
- Firefox now supports the HTML5 video "buffered" property.

4.0 Beta 3
- Web authors can now get touch events from Firefox users on Windows 7 machines.
- A new way of representing values in JavaScript that allows Firefox to execute heavy, numeric code (used for things like graphics and animations) more efficiently.

4.0 Beta 2
- Tabs are now on top by default on Windows and OSX - Linux will be changing when the theme has been modified to support the change.
- You can turn any tab into an "App Tab" by right-clicking on it and selecting "Make into App Tab" from the context menu.
- Web developers can animate content using CSS Transitions.
- Responsiveness and scrolling improvements from the new retained layers layout system.
- JavaScript speed improvements due to engine optimizations.
- Changes to how XPCOM components are registered in order to help startup time and process separation.

4.0 Beta 1
* Tabs are now on top by default on Windows only - OSX and Linux will be changing when the theme has been modified to support the change.
* On Windows Vista and Windows 7 the menu bar has been replaced with the Firefox button.
* You can search for and switch to already open tabs in the Smart Location Bar
* New Addons Manager and extension management API (UI will be changed before final release)
* Significant API improvements are available for JS-ctypes, a foreign function interface for extensions.
* The stop and reload buttons have been merged into a single button on Windows, Mac and Linux.
* The Bookmarks Toolbar has been replaced with a Bookmarks Button by default (you can switch it back if you'd like).
* Crash protection for Windows, Linux, and Mac when there is a crash in the Adobe Flash, Apple Quicktime or Microsoft Silverlight plugins.
* CSS Transitions are partially supported.
* Full WebGL support is included but disabled by default at this time.
* Core Animation rendering model for plugins on Mac OS X. Plugins which also support this rendering model can now draw faster and more efficiently.
* Native support for the HD HTML5 WebM video format.
* An experimental Direct2D rendering backend is available on Windows, turned off by default.
* Web developers can use Websockets for a low complexity, low latency, bidirectional communications API.
* Web developers can update the URL field without reloading the page using HTML History APIs.
* More responsive page rendering using lazy frame construction.
* Link history lookup is done asynchronously to provide better responsiveness during pageload.
* CSS :visited selectors have been changed to block websites from being able to check a user's browsing history.
* New HTML5 parser.
* Support for more HTML5 form controls.