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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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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

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

All Replies (2)

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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?