"Firefox is already running but is not responding" error message - How to fix it

All of your personal settings, bookmarks, and other information are kept in your Firefox profile. To start, Firefox needs an unlocked profile and if it is not the case, it displays the "Firefox is already running, but is not responding" message. This article explains how to prevent this message from showing at startup.

Note: If this is a recurring problem, see Firefox hangs when you quit it for possible causes and solutions.

End Firefox processes

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.

Instead of restarting your computer, you can also use the Windows Task Manager to close the existing Firefox process:

1. Right-click on an empty spot in the Windows task bar and select Task Manager (or pressCtrl+Shift+Esc).
2. When the Windows Task Manager opens, select the Processes tab.
   
    
3. Select the entry for firefox.exe (press F on the keyboard to find it) and click End Process.
4. Click Yes in the "Task Manager Warning" dialog that appears.
5. Repeat the above steps to end any additional firefox.exe processes, if more than one entry is found, then exit the Windows Task Manager.
6. Start Firefox normally.