https://support.mozilla.com/en-US/kb/Firefox%20hangs
See hang-at-exit

Here's a bit more info - I loaded Firefox and opened my email (gmail) then I got no response when I clicked to open a message. I shut down the browser and opened the task manager. Sure enough, there was Firefox. I tried to stop the process, but no response to that. I was able to open IE and my email. Found your reply (thank you very much!) and decided to try some of the steps. In the meantime, I had to manually turn off my pc to get rid of Firefox. Rebooted and am using IE to print out some of the help items to work on. I will let you know how it works.I am going to try some of the steps mentioned in your reply. Again, thanks for responding. Pam

Well, phooey! I tried the step where I started Firefox in safe mode. No problems. Ran perfectly. Then I started Firefox and unchecked the hardware acceleration box. I got the same problem. Worked fine for a while, memory usage high (however, it did stop at around 450000kb), started slowing down. I did some searched, used email, went into facebook and worked on my Farmville farm. Then exited the browser and sure enough, the thing was still running in processes. It is running as we speak (I'm using IE now), and I can't stop the process. I will have to turn off the pc power to get rid of it. I'll check some more of your suggestions and get back to you.

I was able to remove an add-on (Greasemonkey) that seemed to make the difference. I had installed it a couple months ago, but it never worked, then I couldn't find how to remove it. Going through all your suggestions, I finally found where I could blast the sucker. So far, things are working. No issues with Firefox hanging around after exiting, still slow, but better. I'm going to call it solved.

Thanks again for the help now I can shop and farm without fear!

Pam