HI, not sure the reason. No information came regarding your Extensions or Video Card Drivers.

Just make sure please give your self a scan : *https://www.malwarebytes.com/

If nothing found and still will not log off please : Try Firefox Safe Mode to TEST & see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

first, Pkshadow, I would like to thank you for your response. Unforunaley (for me), I have already tried all of those suggestions. I have even done a boot time scan. I generally use the 'Guest ' Account when I am online, but when I have used firefox as the Administrator (which is password protected), I have never had this problem. I only encounter this problem when using the guest account. Short of completely wiping my PC clean of firefox and starting over, but then why am I not haveing the same problem under the Admin account? I have only been having this problem for (maybe) three weeks. Could there be a corrupt file. At one time I had to clear firefox cache because of this, but that was a different issue, and I was given step by step instructions so as not to delete something that should not be deleted. I have done all the scans, I have deleted all temp & cache files (that can safely be deleted). It is just not logging off. After I ask ff to 'forget' I go into options and press exit. Then I do a quick 'scan' (Avast) and I am warned that ff will be shut down in order to clean the cache (which should have already been cleaned). I just go ahead and say OK. But then when I log off the PC I get another warning that it is still running and do I want to do a force log off. Yet when I go into task manager, there is nothing running. Again, this only happens in the Guest account (and only with ff). I very rarely use IE, but I tried it to see if I would have the same problem, but IE is not doing this. My concern is as it is still running it seems to be also 'collecting' more cache data as well. I hope that explains it well enough, I am not exactly computer literate. (I don't even know what a video card driver is) If anyone could help, I would appreciate it SO much. Thank you

Hi, ya, well if just scanned with your usual and it was not Malwarebytes please give a try.

Yes does sound strange and it could be in that Guest Profile which you good make another and move some stuff to.

How about trying that get rid of Firefox thing. Please : uninstall Firefox. Then Delete the Mozilla Firefox Folders in C:\Program Files , C:\Program Files(x86) & C:\ProgramData Then restart system. Then run Windows Disk Cleanup. (Note: This should be Pinned and run Weekly, If never done below expect 10's of gig's) Then run it again and click the button that says Cleanup System Files. Note: your Firefox Profile is saved. But you should make a back up before you do :

• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
• https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer

Reinstall with Current Release Firefox 61.0.1 with a Full Version Installer

• https://www.mozilla.org/firefox/all/

Please let us know if this solved your issue or if need further assistance.

Do you see any Firefox processes in the Windows Task Manager?

Are you using "Clear history when Firefox closes"?

cor-el...When 'shut down', there is no firefox in processes, and, yes, I always use the forget everything as well as going into options and clear all history, cache, etc, plus I always use private mode (firefox is set to never remember history). Pkshadow...I did use malwarebytes. I have Avast premium, I keep malwarbytes "sleeping', but I always run a malwarebytes scan once a week. Also, I run disk clean up on a very regular basis. I will not have the time for a few days, but I am going to 'clear' the guest account, once I transfer some files. and see if that works. I opened and ran FF as administrator (in the guest account) and zero problems. Really bizarre. So I am going to, hopefully by Wednesday, completely clear the guest account and start over. Hopefully that will do the trick. Also, I did check the way FF was 'formatted' (add-ons, security, etc) and they were identical for both guest and admin. I will let you know it getting rid of the guest account works. Thank you both for your help. I will update when I have more Again, thank you, wish me luck :)

Hi, some issues with Avast. Try disabling it and see if the issue goes away. I have not heard it doing any thing like this but could be new.

• https://support.mozilla.org/en-US/kb/secure-connection-failed-error-message#w_avast-and-avg-security-products

Hi guys/gals...Thank you for your help. Firefox just stopped working (completely) earlier today so I just shut down my computer, (I had been 'bested' - by a machine :)). When I went to turn it back on I had every intention of doing the full uninstall of everything firefox and starting from scratch. But my pc had a hissy fit and wouldn't let me use my user account and told me to log off, so I did (again). When I logged back on I had no problem getting into user account. I still had every intention of doing the uninstall, but something made me just check to see how things were running. Everything is working as it should. Still have zero idea what was going on - or how it just got 'fixed', (I deleted so many files and did so many scans, I don't know which one came out the winner). I just hope it lasts. And, yes, I have backed up everything! Pkshadow, I have kept ALL your instructions, and file locations....thank you for that, for people like me that is so so helpful. Step, by step, by step, ohh so helpful. So, again, I just want to say thank you. If it should happen again, just straight to the uninstall. I truly do appreciate the help. Thank You.