“Firefox is already running, but is not responding” Bug

January 2, 2009 · Filed Under Windows

When trying to open Firefox, I often get a pretty alarming sounding error message titled “Close Firefox”. The full error message is: “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”.

I can’t find any Firefox process running in order to close it. What’s going on?

When this happens, it means that Firefox hasn’t yet completely shut down yet and done whatsoever state or preference saving is required, witch means your profile is marked as being in use even though it isn’t, so it won’t let you start it up again yet. That’s because Firefox doesn’t allow two instances of itself to run at the same time for the some profile/user; you have to kill any previous Firefox-bin processes before running it again.

However if you have tried to look for firefox.exe in the services tab of the task manager, you will notice that even though the task manager shows Firefox program is not running, the services is.

I’m pretty sure there are a lot of 3^rd party tools that can list or kill processes on Windows (Vista/XP). But here is how to do that using just your cmd line.

1- Start by using “tasklist” command to list tasks and their process id’s type.

2- To killing tasks via cmd line you can use either:

taskkill /f /im appname.exe

taskkill /f /pid appid

N.B: If this Firefox bug happens after doing a Firefox update, use your “Add/remove programs”… and uninstall Firefox, then go to Mozilla website and download the newest full install version and reinstall it. Many times this will fix the problem once and for all.