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Firefox 4 Beta

Beta version 12: released February 25th, 2011

We rely on your feedback to help shape our products, so we've bundled a Feedback Add-on with the Firefox 4 Beta that provides an easy to use Feedback button.

If you want to test Add-ons with Firefox 4 Beta, you will need to install the Add-on Compatibility Reporter first.

About this release

Firefox 4 Beta is based on the Gecko 2.0 Web platform. Please read below for more detailed information about what's new in this version of the beta release, as well as the known issues.

This Firefox 4 Beta is considered to be stable and safe to use for daily web browsing, though the features and content may change before the final product release. At this time many Add-ons may not yet have been tested by their authors to ensure that they are compatible with this release. If you wish to help test Add-on compatibility, please install the Add-on Compatibility Reporter - your favorite Add-on author will appreciate it!

Check out what’s new, the known issues and frequently asked questions about the latest version of Firefox. Please tell us what you think using the feedback tools provided as part of the beta. We appreciate your input!

What’s New in this Firefox 4 Beta

  • 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:

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.

Downloading

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.

Installing

Please note that installing Firefox 4 Beta 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.

Uninstalling

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.

Add-ons and Themes

Add-ons installed with previous versions of Firefox may not yet have been updated by their authors to work with this Firefox 4 Beta. If you wish to help test Add-ons, please install the Add-on Compatibility Reporter - your favorite Add-on author will appreciate it!

Known Issues

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)

Troubleshooting

  • 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.app/Contents/MacOS/
    ./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 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.

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.