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Error message "Firefox is already running but is not responding" - I have read and action the KB - no fix

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  • 31 have this problem
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  • Last reply by cor-el

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So before we start - I have read the KB (https://support.mozilla.org/en-US/kb/firefox-already-running-not-responding) and actioned the advice on how end the processes, delete the parental lock, etc. This gives a temporary but one time only fix and does not resolve the overall issue.

I have also uninstalled and reinstalled the application.

So why do I get the Error message "Firefox is already running but is not responding"?

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See also:

Note that in Firefox 13+ (expected to be released June 5) the parent.lock file is no longer deleted after closing Firefox to make it possible to check for startup crashes, so the presence of that file will in the future no longer indicate a problem.


Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See: