Fix Firefox is already running but is not responding

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Sometimes, when you try to start Firefox, it warns you that Firefox is already running. The message looks like this:

Firefox already works, but does not respond. To open a new window, you must first close the existing Firefox process or restart your system.

Normally, you can simply exit the Firefox process to solve this problem. But sometimes things get more mixed up than usual.

The Firefox patch is already running, but does not respond to the error:

Remove the parent lock

The solution is to delete a hidden and mysterious file called.parentlock. This file is usually located under your home directory in the following location.
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cd ~/.mozilla/firefox/

You should see a folder with a random name (your name will be different), followed by .default, for example: 06agjsjz.default

Get in that folder:
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cd 06agjsjz.default

There should be a file called.parentlock (it is hidden, so type ls -a to see it). Delete it:
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rm .parentlock

Restart Firefox and it should work!

Manual shutdown of the Firefox process

If your operating system does not stop the Firefox process, you must manually stop the existing Firefox process. The following steps will help you exit the Firefox process:

1. Press Ctrl+Shift+Esc simultaneously to open the Task Manager.
2. Go to the Process or Details tab.
3. Right-click on the Firefox.exe process and select the Finish task or Finish process tree option. You can also click on the Finish Task button at the bottom of the Task Manager window.

Click on the “x” button.

You can also try to click on the Close Firefox button in the Firefox dialog box currently running. The developers have integrated a clever trick that runs when you click on the Close button. It will close the dialog box, stop the Firefox processes and automatically restart Firefox after a few seconds.

Checking access rights

Firefox must also have the right to create files in the profile folder. The error may occur if you try to use a profile from a read-only file system (for example, a remote Windows share where “Allow network users to edit my files” is not enabled).

To check if the profile folder has the correct permissions:

• Go to your Firefox profile folder – see Finding your profile without opening Firefox.
• Go to a folder upstairs.
• Hold down the Ctrl key while clicking on the folder in your profile and select Get Information.
• Make sure that Property and Permissions is set to Read and Write.

https://support.mozilla.org/en-US/kb/firefox-already-running-not-responding

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