Does this happen if you close Firefox and immediately try to restart Firefox?

In such a case you can give Firefox more time to close down completely.

Make sure that Firefox closes properly and that there isn't a hanging Firefox or plugin-container process left in the Task Manager.

Use "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: "Firefox > Quit Firefox"; Linux: "Firefox/File > Quit") to close Firefox if you are currently doing that by clicking the close X on the Firefox title bar.

See also:

• https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding
• http://kb.mozillazine.org/Profile_in_use

• http://kb.mozillazine.org/Kill_application

Firefox had been closed for at least 14 hours previous to me trying to open it again. I do get the error if I try to open it too soon after closing, but not in the case I am referring to today and I can understand that sometimes it takes a few seconds longer to close at times, but not 14 hours!

Did you try to use "Firefox or File > Exit Firefox"?

Do you see any firefox.exe processes in the Windows Task Manager?

In that case you need to close (kill) them.

I always close firefox by the 'close' button in the top right corner. I have to use task manager to close Firefox when it becomes unstable, but lets face it, I shouldnt have to mess around as often as I do with closing the program in this manner. I have been experimenting with Chrome on another PC and I do not have this issue with any other browser. I would prefer to stay with Firefox as long as this issue is rectified

This is clearly a design problem, which puts an unnecessary burden on the user, to the extent that some have left or are considering leaving firefox altogether. Ignoring the fact that it should be possible to design a browser to run parallel sessions, the question is how to avoid the problem of a still closing, or faultily closed session from blocking the start of a new session. This does not seem too hard, and if I was familiar with the source code I would have a go. Since there are presumably people who know it well, I will first suggest how it could be improved. If nothing happens for a while, I will have a go myself. The simplest way would be to post a message saying something like "firefox seems to be running - do you really want to start a new session?", and if the user answers positively, to perform the actions which the user is now suggested to perform manually. If firefox is seen to be shutting down already, then a message like "firefox will start when the old session has shut down" could be emitted. If a badly shut-down old session has left some garbage around, and this can be distinguished from a running session, the garbage can just be deleted. If it can't be distinguished from a running session, then either the user could be asked what to do, or (better) a mechanism introduced to allow this distinction to be made (relatively simple).

I have this same issue and is just started in the new version 25.x x. Version 24.x.x was fine. I also use the X in the upper right have corner and always have, no other browser does this to me. I am running Windows 7 Ultimate 64 bit with 32gig ram on an AMD 4.2 gig system. As far as Chrome (I think i will never use that cause I don't like Google crap)

This error happens every day and not just right after closing the browser, it might take 4-6 hours or 5 minutes. Kind of getting tired of opening task manager to close the FireFox.exe *32 (Aurora) and Yes i know it is beta. Please have one of the guru's fix this.

I am trying very hard to resist going to Chome or, horror of horrors, Explorer, but I am at my wits-end. I cannot justify going to the Task Manager every time I need to open Firefox. It's ridiculous. It's like being sick with a terminal desease and being told to take an aspirin.

It seens that for me this happens when I have many tabs (4-6) open at the same time or when I'm in the same session for an extended period of time and surfing heavily. I do use the X to close but I will try the Exit. Although I shouldn't have to do that either, it beats starting the Task Manager.

Thanks for the opportunity to vent.