Mozilla Firefox

• 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
• See the complete changelist from the previous beta

As well as these features from previous Firefox 4 Betas:

• Firefox 4 Beta is available in 77 languages
• 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
• 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
• Speed, functionality, and compatibility improvements to WebGL
• 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

Developers can find out about all the changes and new features at the Mozilla Developer Center.

Mozilla provides Firefox 4 Beta for Windows, Linux, and Mac OS X in a variety of languages. For builds for other systems and languages not provided by Mozilla, see the Contributed Builds section at the end of this document.

You can remove Firefox 4 Beta with the Add/Removes Programs utility on Windows, by moving the Firefox application to the Trash on Mac OS X, or by deleting the containing folder on Linux.

By default, removing Firefox 4 Beta won’t remove your bookmarks, web browsing history, extensions or other add-ons. This data is stored in your profile folder, which can be found by going to the Help menu and selecting Troubleshooting Information.... The button next to the Profile Directory line in Application Basics will open your profile directory in your system's file explorer.

Please note that if you keep your profile, any version of Firefox that you install after removing Firefox 4 Beta will continue to use the bookmarks, web browsing history, add-ons, and other data from this profile folder.

This list covers some of the known problems with Firefox 4 Beta which will be resolved in future versions:

All Systems

• Users visiting Hotmail.com will likely experience repeated reloading of the page. This is an issue on Microsoft's side and will be fixed in a future site update (see bug 627729)
• The popular video site Hulu.com is not displaying content to beta users due to bad "user-agent" detection in their code (see bug 580843)
• Users will experience many incompatibilities with bookmarks and history if they downgrade to any Firefox 4 beta before beta 8. Users can still downgrade back to Firefox 3.6 (see bug 620723 and bug 614439)
• For some users, scrolling in the main GMail window will be slower than usual (see bug 579260)
• The site Formspring is not displaying content to beta users due to bad "user-agent" detection in their code (see bug 620344)
• If you try to start Firefox using a locked profile, it will crash (see bug 573369)
• Users using Firefox Sync with their mobile device will need to update to the latest Firefox 4 beta for mobile

Mac OS X

• The 32bit Microsoft Silverlight plugin fails to load when using a 64bit version of Firefox on Mac OS X 10.6. Sites that depend on the plugin (such as Netflix) will fail to work (see bug 598406)
• This version of the beta will not work on Macintosh hardware with Power PC CPUs (see bug 587799)

Linux and Unix

• The video control buttons may not work when viewing QuickTime videos with libtotem (see bug 625036)
• Users compiling from source might need a newer gcc and libstdc++ as the build requirements have changed (see bug 578880)

1. What can I do to help?

   We need help from developers and the testing community to provide as much feedback as possible to make Firefox even better. Please pick your favorite way to give us your feedback at any time!

2. Where can I get extensions and themes (add-ons)?

   Extensions and Themes can be downloaded from Firefox Add-ons.

3. Who makes Firefox 4 Beta?

   Lots of people. See Help->About Mozilla Firefox, Credits for a list of some of the people who have contributed to Firefox 4 Beta.

4. Where’s the Firefox 4 Beta source code?

   A tarball of the Firefox 4 Beta source code is available for download. The latest development code can be obtained through Mercurial. Firefox-specific source is in mozilla-central's "browser", "toolkit", and "chrome" directories. Please follow the build instructions.

5. Where is the mail client?

   Firefox 4 Beta works with whatever mail client is the default on your system. However, we recommend Mozilla Thunderbird, our next-generation email client and the perfect complement to Firefox.

The following resources contain useful information about Firefox 4 Beta

• Firefox Support Page
• MozillaZine's Knowledge Base
• Developer Information
• SafeBrowsing Service Privacy Policy (for anti-phishing/anti-malware feature)