Nice drop...
Yikes. Sounds like something is corrupted troop. Roll back if you can?
If not that, just do a manual wipe.
Go into C: Program Files: Folder
Find the Mozilla/Firefox and just delete the entire directory.
^^^I believe you should be able to create a back-up file for your bookmarks.
You history will prob get wiped, but do you really need that?
When you checked Task Manager, did you check the box that says:
'Show processes from all users'
If a process is still running under another account, sometimes that will result in the behavior that you originally posted.
When you uninstall make sure to clean your registry before reinstalling, that might help.
Another issue I had was not being able to copy and paste anything in firefox and not being able to save downloaded files, to fix that I renamed firefox.exe to thefox.exe (you can change it to anything you like) and that solved the problem.
You can use CCleaner (free) or find a cracked version of registry mechanic here on the board.HOw do I clean my registry?
Step 1 Go to processes by clicking control alt delete
Step 2 terminate the process firefox.exe
Step 3 reboot your computer
Step 4 open firefox
If that doesn't work, reinstall FF
Yeah that shit had me perplexed like a mofo, I unistalled then ran CC Cleaner and cleaned the registry reinstalled and so far so good.
^^^^^^^^^Either your lock file needs to be deleted or it resides on a bad block.
http://kb.mozillazine.org/Profile_in_use#Remove_the_profile_lock_file