If Firefox processes that remain in memory at exit are a recurring problem, try these solutions:

• A problematic extension can cause the problem, which can be resolved by disabling or uninstalling the extension. For information on diagnosing and fixing problems caused by faulty extensions, see the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article.
• Sometimes Java applets can cause the Firefox process to persist after exit. Try updating Java to the latest version or, if you don't need the Java plugin, you can disable it from the Plugins panel of the Firefox Add-ons window. For more information, see Use the Java plugin to view interactive content on websites.

Probably see "Firefox is already running but is not responding" error - How to fix for other causes and solutions.

Thanks for that. I did see that article when I was browsing earlier and I will try it because it may help Firefox to close quicker. I just wondered whether this was a new or different problem now that Firefox wasn't closing at all...

Please let us know how the article works for you.

Hi Sorry it has taken a while to respond. I'm afraid the article didn't help - it didn't seem to be the same problem. Firefox always seems slow to shut down and, indeed, sometimes you can close it, remember something else you meant to do on the internet and so open it again immediately and a message will appear saying that Firefox is already open - when it clearly isn't!

Anyway...this problem was different. It seemed like Firefox had "got lost". Double clicking to open it would yield nothing. Task Manager would not register it as open. I couldn't successfully un-install it (or re-install or download a new version and install that)

So in the end I backed up all my files and recovered the entire operating system.

Firefox often doesn't close properly if I have been using the Blackboard 'virtual learning environment'. Task Manager always reveals that the Firefox process is still running and Java as well. Killing Java allows Firefox to close. Is there a more elegant way of ensuring that Java isn't going to block Fx from closing, e.g. because an applet is invisibly waiting for something? It would be good to have a way of pre-emptively 'clearing' Java before closing Firefox. (Gryllida's solution of disabling Java altogether isn't suitable, because Blackboard and many other sites need it.) Thanks.

I run Firefox 4.0.1 on various machines with different OSs: Win XP Pro x64, Win 7 Pro x64 and Win XP Pro x32. All behave the same in this respect.

David