I get a message roughly like this:

Firefox is already running, close it or restart

I am on a network so don't have permissions to do anything with sudo and so cannot restart it so I went looking for the .lock file in .mozilla/firefox.

All that is inside is a


In the file it says



This is maddening. Does anyone know how I can find this lock file? Or another way to get Firefox working again?


4 Answers 4


If the below is the error message the OP was getting....

From http://kb.mozillazine.org/Profile_in_use, there should be:

1) A file called .parentlock
2) A symlink called lock
... in (for this OP) ~/.mozilla/firefox/o4k6tgim.default/.

The former is present while Firefox is running to prevent more than one different instance from trying to simultaneously write to the same set of profile files, and if Firefox is not closed cleanly, neither may be removed.

From anywhere in the filesystem (or removing this if pwd reports (for this OP) ~/.mozilla/firefox/o4k6tgim.default), do (for this OP) rm ~/.mozilla/firefox/o4k6tgim.default/.parentlock ~/.mozilla/firefox/o4k6tgim.default/lock` (assuming the first sentence pans out) to remove them, if there isn't a Firefox process running.

More less-authoritative information here.


Try checking out the output from running strace firefox from the command line ...assumming you are running under some type of Linux.

  • how do I do that? Yes it's scientific linuz
    – Magpie
    Dec 6, 2012 at 22:44
  • @Magpie You just run strace firefox and strace will output every system call as it happens. You can filter it a bit and run strace -e open firefox to show all open() calls, and then look for the line where it tries to open its lock file Dec 7, 2012 at 0:21

First use ps | grep firefox to check that the process isn't stuck somewhere. If it is, use kill to terminate it - you'll probably need kill firefox-bin. Once you know Firefox is not running, you can delete the .lock file in the profile.


Thanks for all the suggestions but I did not get to try them to confirm whether they would have worked, as I managed to solve it earlier by going to terminal and hitting

firefox -P

Then i created a new profile.ini and deleted the one there and tried again.

This worked!

  • 1
    NOTE: (For future visitors to this question. The above is a workaround, and (I would think) a more time intensive one, compared to other offered solutions; not a solution.
    – user66001
    Sep 3, 2013 at 1:58

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