· Blacklisted a few invalid HTTPS certificates
· Updated localizations for 29 locales
· Added Vietnamese localization, bringing the total languages available in Firefox 4 to 83
· Support for the proposed Do Not Track ("DNT") header
· Connection status messages are now shown in a small overlay
· WebGL is enabled on all platforms, but, like for other hardware acceleration features, many buggy drivers or driver versions are blocked
· The default homepage design has been refreshed
· Firefox no longer switches into offline mode automatically
· 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
· The Firefox Sync setup experience has been greatly improved across desktop and mobile devices
· Additional polish for the Firefox Add-ons Manager
· Uses JägerMonkey, a new, faster JavaScript engine
· 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
· 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
· 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
· Tabs are now on top by default on Windows, Mac OS X, and Linux
· 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
· 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 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
· CSS Transitions are partially supported
· Full WebGL support is included
· 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
· 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