Browser will not start up

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Template:Test File names and program names are different for Mozilla Suite.

If you are trying to run Firefox for the first time, then you should look at the Firefox FAQs.

Purpose: If Firefox used to work correctly, but it no longer starts when you try to run it, then this article may help. Before deleting anything, please back up your profile.


The Profile Manager/Profile In Use Bug

If you receive the "profile is in use" error when trying to launch the application, this means the profile is locked. See the Profile in use article for how to fix this.

The Mac Firefox Bug

From's Firefox 0.9 Release Notes:

If Firefox will not display a browser window on Mac OS X, quit Firefox using "Cmd+Q" and open your profile folder and remove the "localstore.rdf" file. Restart Firefox. Note: Any toolbar customizations you have made or window placement will be lost.

How to Make Firefox Start

  1. Completely close Firefox.
  2. Make sure Firefox is not running in the backround.
    • In Windows, hit Ctrl+Alt+Del, open the Task Manager, view Processes, and make sure firefox.exe is not there. If it is, click on it and End Process. Run Firefox again. If everything goes smoothly, then you can stop. If it doesn't and it hangs invisibly again, repeat the process and try opening it in Safe Mode (see below) next time.
  3. Firefox only. Run Firefox in safe mode. Disable your extensions via Tools -> Extensions. If it starts up now, it's an extension problem, and you should try isolating which extension is causing it. Once you do, keep that extension disabled or uninstall it.
    • For Mozilla users and users that don't want to isolate the extension, try the "Clearing Extensions and Themes" trick below.
  4. Browse to your profile folder.
  5. Delete XUL.mfl (also known as "xul.mfasl") from your profile. This file will be regenerated next time you start Firefox.
  6. Delete the Cache folder.
  7. Try running Firefox.
  8. If Firefox still does not work, then more drastic measures may have to be taken. Before continuing, be sure to back up your profile.
  9. At this point, it is usually best to create a new profile.

Clearing Extensions and Themes

Firefox only: If you can run Firefox in safe mode, then the source of your problem is your extensions.

All you have to do is delete your "extensions" and "chrome" folders in your profile. Note that you will lose all your extensions and themes.

Firefox Still Won't Start

  1. Make sure to back up your profile and then completely remove your profile folder.
  2. Uninstall Firefox.
  3. Reinstall Firefox.

Firefox Starts But My Settings Are Gone

  1. Make sure you're using the correct profile. Run the Profile Manager and select the default profile.
  2. If that wasn't your problem and you have backed up your profile, you should be able to simply copy the backed up files to your new profile. See "What do I do if my profile's corrupted?" for help on doing this.
  3. If you are missing themes or extensions, you will have to reinstall them from scratch.