All of your personal settings, bookmarks, and other information are kept in your Firefox profile.

• For more information on Firefox profiles, see the Profiles article.

Firefox will only use one profile at a time. It does this by putting a lock file in your profile folder when it starts. When you exit Firefox, the lock file is removed. If the lock file already exists when you start Firefox, or in a few other cases where the profile cannot be opened, Firefox displays an error message: "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."

Table Of Contents

• The previous Firefox session did not close
• Firefox did not shut down normally
• Profile folder is unavailable
• Access rights
• Restoring data from a locked profile

Firefox did not shut down normally

If Firefox did not shut down normally when you last used it, Firefox might still be running in the background, even though it is not visible. Restart your computer to see if the problem goes away.

Note: If this is a recurring problem, see Firefox hangs - Hang at exit for possible causes and solutions.

If simply restarting didn't help, it may be that Firefox previously exited without deleting the lock file.

1. Restart your computer. After it restarts, don't try to start Firefox.
2. Open the profile folder.
   • For information on finding your profile folder, see Profiles.
3. Delete the lock file parent.lock.parentlock
   • If you attempt to delete the parent.lock file and receive the error, "Cannot delete parent: The file or directory is corrupted and unreadable", restart the computer and run the error-checking tool Chkdsk (Windows 2000, XP) or ScanDisk (Windows 98, ME)You need to use a free utility like Onyx or Maintain to turn on visibility for invisible files to show .parentlock. This file contains no information, and deleting it will unlock the profile.You will need to turn on the display of hidden files. In the File Browser window, select the View menu and make sure Show Hidden Files is checked.

Profile folder is unavailable

If Firefox cannot find the profile folder, it will report that the profile is in use or already running. This can happen if you delete, rename or move the profile folder; if you run Firefox from removable media; or if the profile folder is stored on a network drive. Make sure the profile folder is still accessible.

Access rights

Firefox must also have the right to create files in the profile folder. This can happen if you try to use a profile from a file system mounted with read-only (e.g. a remote Windows share which doesn't have "Allow network users to change my files" checked).

To check if the profile folder has the proper permissions:

Restoring data from a locked profile

If you are unable to unlock the profile using the above methods, use the Profile Manager to create a new profile and migrate your data from the locked profile to the new profile.

• For information on how, see Recovering important data from an old profile.

Based on information from Profile in use (mozillaZine KB)