from the mozillazine forums ...
OK: That was the 'hanging' firefox.exe 'process' still running on your system. Do the following:
Open Task Manager (ctrl-alt-del) and look in the 'processes' list and if you find 'firefox.exe' then highlight it and click on 'end task'.
Start > run, and type in: firefox.exe -p
That is firefox.exep
That should launch Profile Manager and you should see TWO profiles listed. The original 'default' one has all your old settings. Delete the new one you created and launch with the old one.
If the above path doesn't launch Profile Manager, you may need to enter it as follows instead:
Start > run > firefox.exe -ProfileManager
If ever you get asked, out of the blue, to create a new Profile, don't. Just do the 'Task Manager' thing above and you can launch normally.
Good luck. Smile