Please explain, what happend? Does anyone know how to fix that?
Thnx 
reinstalling not works 
Is it this addon: https://addons.mozilla.org/en-US/firefox/addon/gmail-notifier-restartless/
Maybe another one of youraddons is getting in the way. To test things, make a new profile with this addon: https://addons.mozilla.org/en-US/firefox/addon/profilist/
Then innstall gmail notifier here and see if it works, if it doesnt, then we’ll get in touch with the addon author. If it does, then in your original profile we’ll deactivate one addon at a time, restrat, until we get notifier addon working.