Firefox Profile in Use

From time to time I receive an error message stating that Firefox is having issues starting up after I close it or after it crashes. There are two different error messages that I receive the most, and today we’re going to cover a few different ways that will hopefully bring your Firefox back to life.

Here are the two errors that you might see:

  1. 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.
  2. Firefox cannot use the profile <profile name> because it is in use. To continue, close the running instance of Firefox or choose a different profile.

The first error message you’ll likely see only after closing and then trying to reopen Firefox. It will appear as though Firefox was shutdown, but the computer was not actually able to close it. The easiest way to solve this issue is to open up the list of running processes (on Windows that is Ctrl+Alt+Del), and find firefox.exe in the list. Then end the process to forcefully close Firefox. Or you can just restart your computer.

The “profile in use” error message is a little bit trickier to solve. The first thing that you’ll need to do is locate the Firefox profile on your computer:

Operating System Profile folder location(s)
Windows 95/98/Me

C:\Windows\Application Data\Mozilla\Firefox\Profiles\

C:\Windows\Profiles\<Windows login/user name>\Application Data\Mozilla\Firefox\Profiles\

Windows NT 4.x C:\Winnt\Profiles\<Windows login/user name>\Application Data\Mozilla\Firefox\Profiles\
Windows 2000 and XP C:\Documents and Settings\<Windows login/user name>\Application Data\Mozilla\Firefox\Profiles\
Windows Vista C:\Users\<Windows login/user name>\AppData\Roaming\Mozilla\Firefox\Profiles\


Mac OS X


~/Library/Application Support/Firefox/Profiles/

Once you find your profile’s folder there will be a file in it that you need to delete. The file is a “lock” that the browser creates to ensure that no other applications are able to modify the files while Firefox is using them. Here’s the name of the file you’ll be looking for:

  • On Windows the file is named parent.lock
  • On Linux there are two files: lock and .parentlock
  • On Mac OS X the file is named .parentlock

Once the file is deleted you should be able to open up Firefox without any issues.