Does the window itself close when you try to close it?

Try closing Firefox, via File > Exit

The previous suggestion of File > Exit won't work as a fix. The problem is the Firefox process won't exit. Another suggestion has been to delete the parent.lock file in the profile folder under Users, but that doesn't work either.

I went so far as to totally remove Firefox from my system, delete existing profiles and start with a clean new vanilla install of Firefox 26. It still does it.

Hi drkenrich, in your clean install, Firefox will grab plugins and extensions listed in the registry. Do you want to try disabling those on the Add-ons page?

Failure to shut down could indicate a problem with some external software on your computer. Over the years, various security products have caused Firefox to hang during shutdown, including some referenced in this article:

http://kb.mozillazine.org/Firefox_hangs#Hang_at_exit

I'm not suggesting disabling disabling your security software, but perhaps it has some feature that isn't fully compatible with Firefox?

I appreciate the suggestion. I did a variation on this that seems to be working now.

I worked backward to a clean install by disabling all my add-on AND resetting Firefox. Once that was done, it unloaded properly.

Next, I opened a window of Task Manager to remain open. Then I opened Firefox and installed ONE add-on at a time. After each add-on I went through a couple of links and tabs before closing Firefox and watching Task Manager to see if the process closed. By doing this I was able to get all the add-ons and options working properly.

I didn't run into a specific conflict but I did find that two different add-ons I was running covered the same settings so I only used one. So far it's now working.

I've explained the process so others can try it on their problems.

Thanks, Dr. Ken Rich

I had the very same problem and posted below. I included a fix for my system that seems to be working and give directions to others on how to do the same thing.

Hope it helps.

Dr. Ken Rich

IT'S BAAAACK!!

I thought I'd fixed it with the above. It worked for about a week and now the problem's back. I guess what I did didn't work.

Maybe, someone else can help us all.

Did the article help at all?

http://kb.mozillazine.org/Firefox_hangs#Hang_at_exit

SOLUTION (possible).

Hi all. I had this problem as well. I currently run FF26. A week or so ago, out of nowhere FF wouldn't exit - the window would close but firefox.exe process would keep running in the background using about 50% of CPU. Not sure if it's connected, but just prior to that I clicked on a link on Facebook that looked like spam website, nothing happened, site loaded (sort of, all I saw was a msg - Please Wait...) but nothing happened, I have Eset antivirus and it monitors network traffic and files for viruses, so maybe it prevented my PC getting infected...

So, I had this problem for a few days, was searching the net for solutions, but nothing seem to help. Then, just out of luck I did something that WORKED!

Here's what I did. I noticed that svchost.exe was using a lot of CPU alongside with FF. I ran ProcessExplorer to see what might be connected to this process, the list was long and I didn't have any idea where to start, so what I did was - Right click on svchost process, choose Debug and dismiss the warning. In a few seconds svchost process quit and after that FF started closing properly.

I had to re-enable all my plugins and themes I disabled prior, I also lost my history and preferences which I trashed in the process of searching for solution. But heck, it worked, hopefully for good. Now if someone could point out the real cause of this and fix it for everyone - that would be great. Cheers!

This is like the blind leading the blind. I wish a knowledgeable tech would weigh in on this.

I reported above my efforts and failures.

Laserbeam, thank you for your input. I used ProcessExplorer to do what you did with different results. Firefox kept showing up under the ProcExp tree with nothing else involved while debugging it. Outside of the debugging it showed up as it's own process with no attachments. So, something isn't correct.

I've been playing with various add-ons and have found this pattern. I've narrowed it down to one of three that I can't isolate. Adblock Plus 2.4 Block site 1.1.8 Blocksite Plus 1.1 When I install any one of them, nothing bad happens for about 3 or 4 days, no matter how many times I open/close/reset Firefox or my computer. Then it starts the problem again. When I remove the add-on it takes about that same time before it returns to normal.

I'm not a programmer. I just hack away at things. But, this seems to indicate there may be something wrong with this build, not with a virus or offending add-on. At this point I've added Windows Task Manager to my Start Menu so I can quickly clear the Firefox process.

Frankly, this is why I generally stay away from the most current updates regardless of all the fancy new bells and whistles. I think I'll go back to an earlier version. Here's the link if anyone else decides to do this. http://ftp.mozilla.org/pub/mozilla.org/mozilla.org/firefox/releases/

Well drkenrich, without any solid info as to why this is happening no tech would be able to provide any help, this is why I posted what worked for me. Maybe eventually a lightbulb will light up in someone's head and solution will be found.

From what you posted I can confirm that I also have Adblock Plus 2.4 installed. And just to make sure, I debugged svchost.exe, not firefox process. Best.