"No longer"? When did it stop working? What changed, do you think? Does it all work if you login directly to the gmail website? Are you using OAuth2 and IMAP in Thunderbird with your gmail account? Thunderbird stores passwords under '''[http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac Tools|Options]|Security|Passwords→Saved Passwords'''. Here you can delete a password, and in theory when Thunderbird needs it and can't find it, you'll be asked to re-enter it. Take care to find and delete ALL instances of the password. Use the search box at the top of the passwords box to show them.