For over a week I've not been able to open FF--I get a message that says "FF is already running but is not responding. To open a new window, you must first close the existing FF process, or restart your system." I've tried the following: scanning my computer completely for malware and viruses (got rid of all threats); going into Task Manager and looking for multiple versions of the mozilla.exe or firefox.exe (in fact there were none at all listed); downloading various versions of FF (3, 4, and 5). None of this has made a difference. I've been using Google Chrome for some time, as a result. But all my bookmarks are in FF, and they're very necessary for my work. I also like FF.

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Maybe a stupid question, but since you did not mention it, did you try rebooting the computer? Whenever I get that issue with firefox, a reboot fixes it.

Maybe a stupid question, but since you did not mention it, did you try rebooting the computer? Whenever I get that issue with firefox, a reboot fixes it.

Hi, I realized after posting the thread that I didn't include that as one of my troubleshooting procedures--yes, I rebooted it numerous times each day (for the past 11 days or so). In fact, the problem got worse: FF at first would at least open up for about 15 minutes or so and then start having problems. But as of a week ago it wouldn't even open up anymore!

Do a scan with Malware Bytes first. Use the free version

Export your bookmarks out of Firefox if you cannot even use firefox use another browser to help you. Use Chrome or Internet Explorer and import firefox bookmarks and data.

See this link to help you import booksmarks to chrome from another browser. Good luck and hope to hear a reply from you soon.


Try the following:

Restart your computer.
After it restarts, don't try to start Firefox.
Go to your Firefox profile folder in the appdata (or type this in your search box - %APPDATA%\Mozilla\Firefox\Profiles\). Get the xxxx.default profile open.
Delete the lock file parent.lock

If this cannot be deleted, either the profile is unavailable for FF or a problem with the partition. Make sure the profile is not read only.

If these methods do not support to solve the issue, you have to create a new profile and migrate to the new one. Use this link to learn how to. Hope this helps :)

Maybe you just need a complete firefox reinstallation (uninstall and reinstall)

Just in case, copy all files under C:/Program Files/Mozilla Firefox/ and paste it somewhere else. Then uninstall Firefox using normal uninstall or Revo. Make sure firefox program is completely uninstall... Then reboot...

Then download firefox 5 (latest one) and install it. After install, don't try to open firefox just yet, reboot once and then try to open firefox...

See whether this helps...

This may occur many times. when you close your browser. and instantly open it second time. is shows this error. or if it is not properly closed. error occurred.

For that you can check you task manager firefox.exe process is running and not closed exactly. So right click End task And Start Again Firefox.

It may works most of time. other wise Reinstall it.

Press Ctrl+Alt+Del
Click on process tab
locate that whether firefox process is running or not... it is running right click on it and click on end process... now try to run Firefox.

I usually find manually clearing the cache in %APPDATA%\Local\Mozilla\Firefox\Profiles\xxxxxxxx.default helps. Delete everything in there- FF will rebuild it when it starts again.

Make sure you delete the correct folder contents. Only the folders and files in the default profile that contain the cache folders. Should look something like this-

The solution mentioned above will solve the issue. If you have a doubt like it is using by other application, you have to disable recently added plugins. To check whether it is locked by a process you can use a process viewer or something run something like LockHunter against the executable (firefox.exe) file

Have you solved the problem? If so, how? It might help other FF users.

Go To Start>Run>"%APPDATA%/Mozilla/Firefox/"
Open "Profiles.INI"


If it is 1 then change it to 0.
Now Open Firefox
A Window will open.
Choose "Default" and Chech "Do Not Start At Startup" and click "Start Firefox"

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