Since uninstalling FireFox 4, I can no longer start any version of FireFox
FireFox 4 does not work correctly with php session_start() on our website, so I uninstalled it to go back to 3.6. Now, no version of FireFox, including 3.6 and 4 will run on my system. They give me the error:
"Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."
Task Manager shows no instance of Firefox running. Restarting the system did not fix it. The only thing I did not do on uninstalling Firefox 4 was to delete my preferences. I have about 27 tabs open on 3 instances of Firefox and I do not want to lose those.
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Press CTRL+SHIFT+ESC to launch Windows Task Manager, go to to the Processes tab and look for firefox.exe. If it's there, right click it and choose "Kill Process".
What I suggest you do after that is to uninstall/reinstall it again as follows. I've provided links to both FF4 and the previous secure version, so you can choose either. Also, I suggest downloading it with either IE8 or 9 and then saving the file to your desktop when you see the prompt.
Go to Download Firefox 4.0
Then go to Add/Remove Programs, scroll down to Mozilla Firefox and remove it, choosing to keep your bookmarks, customizations etc., (don't checkmark the box).
Then reboot and delete the folder called Mozilla Firefox at this location: C:\Program Files\Mozilla Firefox
Finally run the installation file you downloaded to the desktop earlier.
Your bookmarks, customizations etc., are maintained in a different location and will become available to you again once you complete the installation.
Thanks. I had already used the Task Manager to look for Firefox processes and there were none. I had reboot multiple times. I finally went through the Registry and deleted all references to Firefox that were there, then I was able to reinstall Firefox.