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Firefox 3.1 Beta 3
Release Notes

released March 12th, 2009 This is the fifth development milestone and third beta release of Firefox 3.1, the upcoming version of the Firefox web browser. Please read below for more information.

About this Beta

Firefox 3.1 Beta 3 is the fifth development milestone and third beta release of Firefox 3.1, the next version of the Firefox web browser. While this release is considered to be stable, it is intended for developers and members of our testing community to use for early evaluation and feedback. Users of the latest released version of Firefox should not expect all of their add-ons to work properly with this beta.

Check out what’s new, the known issues and frequently asked questions about the latest version of Firefox. As always, you’re encouraged to tell us what you think, either using this feedback form or by filing a bug in Bugzilla.

What’s New in Firefox 3.1 Beta 3

Firefox 3.1 Beta 3 is based on the Gecko 1.9.1 rendering platform, which has been under development for the past 9 months. Firefox 3.1 is an incremental release on the previous version with significant changes to improve web compatibility, performance, and ease of use:

  • This beta is now available in 64 languages - get your local version.
  • Improved the new Private Browsing Mode.
  • Improvements to web worker thread support.
  • Improved performance and stability with the new TraceMonkey JavaScript engine.
  • New native JSON support.
  • Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
  • Support for new web technologies such as the <video> and <audio> elements, the W3C Geolocation API, JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications.

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

System Requirements

Before installing, make sure your computer meets the system requirements.


Mozilla provides Firefox 3.1 Beta 3 for Windows, Linux, and Mac OS X in a variety of languages. You can get the latest version of Firefox 3.1 Beta 3 here. For builds for other systems and languages not provided by, see the Contributed Builds section at the end of this document.


Please note that installing Firefox 3.1 Beta 3 will not overwrite your existing installation of Firefox. You won’t lose any of your bookmarks or browsing history, but some of your extensions and other add-ons might not work until updates for them are made available.


You can remove Firefox 3.1 Beta 3 through the Control Panel in the Start Menu on Windows, by removing the Firefox application on OS X, or by removing the firefox folder on Linux.

Removing Firefox 3.1 Beta 3 won’t remove your bookmarks, web browsing history, extensions or other add-ons. This data is stored in your profile folder, which is located in one of the following locations depending on your operating system:

Windows Vista Users\<UserName>\AppData\Roaming\Mozilla\Firefox
Windows 2000, XP, Server 2003 Documents and Settings\<UserName>\Application Data\Mozilla\Firefox
Mac OS X ~/Library/Application Support/Firefox
Linux and Unix systems ~/.mozilla/firefox

Any version of Firefox that you install after removing Firefox 3.1 Beta 3 will continue to use the data from this profile folder.

Extensions and Themes

Extensions installed under Firefox 3 may be incompatible and/or require updates to work with Firefox 3.1 Beta 3. Please report any issues to the maintainer of the extension. When you install Firefox 3.1 Beta 3 all of your Extensions and Themes will be disabled until Firefox 3.1 Beta 3 determines that either a) they are compatible with the Firefox 3.1 Beta 3 release or b) there are newer versions available that are compatible.

Known Issues

This list covers some of the known problems with Firefox 3.1 Beta 3. Please read this before reporting any new bugs.

All Systems
  • Dragging a tab onto the desktop doesn't create a new window (see bug 475066)
  • Occasionally Google Mail will fail to respond when creating a new filter, showing advanced search options, or clearing the spam folder. Reloading Google Mail fixes the issue (see bug 477101 and bug 478778)
  • When returning from Private Browsing Mode, some sites served over SSL will not load properly (see bug 463256)
  • Some users with older computers or slower Internet connections may experience choppy OGG video/audio playback (see bug 462667)
  • Users who run this beta, then downgrade to a previous Firefox 3.1 Alpha or Beta, will be unable to use stored passwords (see bug 467463)
Microsoft Windows
  • If you are using MS Natural Input 2002 v8.1, IME will automatically activate when certain text fields are focused. This is a known Microsoft issue (see bug 478882)


  • Poorly designed or incompatible extensions can cause problems with your browser, including make it crash, slow down page display, etc. If you encounter strange problems relating to parts of the browser no longer working, the browser not starting, windows with strange or distorted appearance, degraded performance, etc, you may be suffering from Extension or Theme trouble. Restart the browser in Safe Mode. On Windows, start using the "Safe Mode" shortcut created in your Start menu or by running firefox.exe -safe-mode. On Linux, start with ./firefox -safe-mode and on Mac OS X, run:

    cd /Applications/
    ./firefox-bin -safe-mode

    When started in Safe Mode all extensions are disabled and the Default theme is used. Disable the Extension/Theme that is causing trouble and then start normally.
  • If you uninstall an extension that is installed with your user profile (i.e. you installed it from a Web page) and then wish to install it for all user profiles using the -install-global-extension command line flag, you must restart the browser once to cleanse the profile extensions datasource of traces of that extension before installing with the switch. If you do not do this you may end up with a jammed entry in the Extensions list and will be unable to install the extension globally.
  • If you encounter strange problems relating to bookmarks, downloads, window placement, toolbars, history, or other settings, it is recommended that you try creating a new profile and attempting to reproduce the problem before filing bugs. Create a new profile by running Firefox with the -P command line argument, choose the "Manage Profiles" button and then choose "Create Profile...". Migrate your settings files (Bookmarks, Saved Passwords, etc) over one by one, checking each time to see if the problems resurface. If you do find a particular profile data file is causing a problem, file a bug and attach the file.

Frequently Asked Questions

  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 read these notes and the bug filing instructions before reporting any bugs to Bugzilla. You can also give us your feedback through this feedback form.

  2. Why haven’t you responded to the mail I sent you?

    Use the newsgroup. The Firefox team reads it regularly, and your email may have gotten lost.

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

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

  4. Who makes Firefox 3.1 Beta 3?

    Lots of people. See Help->About Mozilla Firefox, Credits for a list of some of the people who have contributed to Firefox 3.1 Beta 3.

  5. Where’s the Firefox 3.1 Beta 3 source code?

    A tarball of the Firefox 3.1 Beta 3 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.

  6. Where is the mail client?

    Firefox 3.1 Beta 3 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.

Contributed Builds

These are unofficial builds and may be configured differently than the official Mozilla builds. They may also be optimized and/or tested for specific platforms. You can browse through the available contributed builds on the FTP site.