Thanks to Gmail Manager you will not have to be checking your e-mail account each two minutes to see if that desired email have arrived. Now, Gmail manager will advise you when a new e-mail have arrived. But that is not the only function of Gmail manager.
It displays account details including unread messages, saved drafts, spam messages, labels with new mail, space used, and new mail snippets. And you can control more than one account.
Without any doubt Gmail manager is a very good choice if you have a Gmail account and use firefox as your browser.