Firefox/Thunderbird "already running, but is not responding"

Firefox and Thunderbird create lock files when they start to ensure if you run them twice you do not corrupt your settings. If the application exits unexpectedly, then the lock files remain in place and you get this warning. Restarting the machine will have no effect and is generally not a good first step as you could cause hardware damage or loss of work for others.

The correct fix is to remove lock files (assuming you are sure the application is not running). On the Linux computers, you can run the commands:

For Firefox/Iceweasel: rm -i ~/.mozilla/firefox/*/.parentlock ~/.mozilla/firefox/*/lock

For Thunderbird/Icedove: rm -i ~/.mozilla-thunderbird/*/.parentlock ~/.mozilla-thunderbird/*/lock

Further reading:

• http://kb.mozillazine.org/Profile_in_use
• http://kb.mozillazine.org/Browser_will_not_start_up
• http://support.mozilla.com/kb/Firefox+is+already+running+but+is+not+resp...

Related topics are

• http://kb.mozillazine.org/Lost_bookmarks - for info on recovering lost bookmarks
• http://kb.mozillazine.org/Locked_or_damaged_places.sqlite - can't edit or delete certain bookmarks, you can't add new bookmarks, your history is missing, the back/forward toolbar buttons are disabled