Running Mac OSX 10.7 . I am unable to uninstall the StumbleUpon 3.7 add-on - I have tried uninstalling from the tools menu but when I relaunch Firefox the StumbleUpon toolbar is still present & the add-on is listed as disabled in the Tools menu. I have tried trashing the folder in ~/Library/Application Support with the same consequences. I have tried downloading and reinstalling the extension but encounter an error message that Firefox cannot modify the needed file. Every time I launch Firefox the "cannot restore session" error message is displayed and Firefox stalls and hangs the machine. Often an error message indicating that a running script cannot complete is displayed. The message window describes a script beginning, I believe, "Chrome:StumbleUpon...". I am not certain since I disabled the alert hoping that might help to resolve the problem.