This site will have limited functionality while we undergo maintenance to improve your experience. If an article doesn't solve your issue and you want to ask a question, we have our support community waiting to help you at @FirefoxSupport on Twitter and/r/firefox on Reddit.

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

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

  • 1 reply
  • 31 have this problem
  • 2 views
  • Last reply by cor-el

more options

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"?

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"?

All Replies (1)

more options

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: