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Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window.

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  • Last reply by jscher2000

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Hello,

I've been trying to open Firefox and receiving the error "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window.

I've checked the task manager, restarted the computer, re-installed, refreshed and nothing helps, still getting the same error. Any suggestions? Thank you

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Helpful?

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In the Windows 7 Task Manager, click over to the Processes tab and sort by process name to see whether any instances of firefox.exe can be found.

If not, there may be a lock on a specific file in the profile folder. This is mentioned in the help article ("Firefox is already running but is not responding" error - How to fix), but let me spell it out in more detail.

To investigate, you can use this shortcut path in the Windows search box on the Start menu:

%APPDATA%\Moziila\Firefox\Profiles

That should launch Windows (File) Explorer here:

C:\Users\username\AppData\Roaming\Moziila\Firefox\Profiles

(Since AppData is a hidden folder, the shortcut is a good way to jump in there.)

So you might find one or more subfolders here. The naming pattern is a random part followed by a dot followed by a readable part, like:

fpvyp59t.default

In each subfolder, check for this file:

parent.lock

Try deleting that file.

Assuming you can, then try starting Firefox. Success?

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