Hello,

This could happen sometimes if some plugin didn't shutdown cleanly. You will need to end the processes in the task manager to be able to launch Firefox. If you have enabled Firefox to restart with the previous session, the session would get restored. Please try that and check if you are able to launch Firefox.

Thank you

I have been killing the processes and restarting without problem (although killing 26 instances is tedious). I was hoping to be able to prevent in the future.

Any thoughts on which add-ons might br a problem?

See:

• https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding
• http://kb.mozillazine.org/Profile_in_use

See also:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

See:

• "Hang at exit": http://kb.mozillazine.org/Firefox_hangs
• "Firefox hangs when you quit it": https://support.mozilla.org/kb/Firefox+hangs

Firefox sometimes needs more time to close and it is also possible that Firefox fails to close properly and that there is a hanging Firefox or plugin-container process showing in the Task Manager.

• Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit) to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

Are you using "Clear history when Firefox closes"?

• Tools > Options > Privacy > Firefox will: "Use custom settings for history": [X] "Clear history when Firefox closes" > Settings
• https://support.mozilla.org/kb/Clear+Recent+History

I did not have this problem until upgrading to 26. It may have something to do with my custom cache size of 100MB. I have deleted the parent.lock file as above but it was 0 KB. I am hoping this stops.

Hello Axis,

Can you please confirm if this happens each time you are using Firefox? Also, the cache size wouldn't have a big bearing on this issue happening. Can you please try if this issue happens when you are running Firefox in safe-mode (instructions below). if it doesn't then we can narrow the issue to a plugin / addon.

Safe Mode is a troubleshooting mode, which disables most add-ons. (If you're not using it, switch to the Default theme.)

• On Windows you can open Firefox 4.0+ in Safe Mode by holding the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac you can open Firefox 4.0+ in Safe Mode by holding the option key while starting Firefox.
• On Linux you can open Firefox 4.0+ in Safe Mode by quitting Firefox and then going to your Terminal and running: firefox -safe-mode (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)
• Or open the Help menu and click on the Restart with Add-ons Disabled... menu item while Firefox is running.

Once you get the pop-up, just select "'Start in Safe Mode"

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, and you need to figure out which one. Please follow the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article for that.

To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help other users who have the same problem.

Thank you.

Hello gnittala--

Things seem to have straightened out. I was going through an avalanche of updates all on the same day (not firefox) and cleaning up behind them. I think that probably made my system "wobbly" or something. I have had no further issues with this since posting earlier. Thanks.