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Firefox is already running, but is not responding...

If you get this frustrating message after starting up your Firefox browser, there are two possibilities that could be the problem. To troubleshoot, just follow the steps on this page.  If you installed add-ons in Firefox, I would try Fix #2 on this page before Fix #1.

In order to fix this problem, you have to stop Firefox from running in the background by using "Task Manager" before doing the fix.

To Open Task Manager:

  1. Right-click on an empty spot on your taskbar and click on "Task Manager".  This is the same Task Manager that you would get when you used to press "Ctrl + Alt + Delete" in Windows XP.
  2. When "Windows Task Manager" pops up, click on "Processes" (second tab from left)
  3. In the "Description" section, you should see a reference to Firefox.  Single click on it and click "End Process".  Close "Windows Task Manager".

Now on to Fix #1 (out of 2 possibilities)

  1. Click on the "Start" button
  2. Type "appdata" (without the quotations) in the "Start Search" bar.  Click on "appdata" when you see it appear above.
  3. Open the Roaming folder.
  4. Navigate to Mozilla folder and open it.
  5. Open "Firefox" folder.
  6. Open Profiles and open the next folder you see inside.
  7. Navigate to the "parent.lock" file and delete it.  If you don't see it, then Firefox closed it out when you shut down the process in Task Manager, which is what Firefox is supposed to do.

This (according the the Mozilla Knowledgebase) should fix your problem.  To find out, simply open Firefox, close it and then open it again.  If it opens, your problem is fixed.

*However if you get the same message AGAIN, it is extremely likely that one of your latest add-ons is causing the problem.  To eliminate them one by one, you can try:

Fix #2

  1. Stop Mozilla Firefox from running in the background by using "Task Manager" as above (right-click Taskbar, click on Task Manager, click Processes, click Firefox, click End Process) and then close Task Manager.
  2. Open Firefox browser
  3. Click on "Tools" (top left, second last option)
  4. Click "Add-ons"
  5. Click on your latest add-on and click "Disable"
  6. Restart Firefox, close it out and then restart it again.

If your message is still there, continue the above steps eliminating the add-ons from the newest to the oldest.  If or when you've found the faulty add-on, go back and uninstall it.  It's highly probable that your problem will be solved.  I know that mine was.

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Fix for error message "Firefox is already running, but is not responding..."