Then type "ps -ef | grep firefox" then enter.
Note the PID on the left then type "kill [PID #]
Firefox will be gone.
If you run Windows...Task manager is your only option I think.
With that being said, I finally had to uninstall Firefox but kept getting the prompt that it was still running even tho I had on several tries used task manager to delete it.
I finally resorted to using System Restore to a prior date and that really screwed up my computer. Got error messages after the restore saying there were problems, to restart computer but when I did, it never fully restarted and would shut down.
Finally got another screen that took me to the "restore system" again and that gave me the option to reverse what I had just done.
FWIW, this was taking me hours.......
Anyway, what I had unrestored was restored to the original state of last night.
I was finally able to reinstall Firefox but lost all of my bookmarked websites due to my not saving them somewhere............
So the newer version of Firefox is now installed but it is totally unrecognizable and I have to continue to find and bookmark all the sites that were deleted...........
Anyway, it's back to normal but now another pain in the ass that I have to learn how to manage..............
I have to admit, I suffered extreme anxiety over the loss of the use of my computer since I am on it all day long. It wasn't the loss of the computer but how the hell am I going to fix it.
That's a bad sign that we are becoming addicted to technology..........