Thunderbird is a program - you do not logon to Thunderbird. Perhaps you have mail accounts and it is asking for password to access server. ''re :I have followed all the instructions, made the appropriate changes, '' You need to remember that no one can see your computer nor what mail accounts you have in Thunderbird. What Operating System are you using ? what version of Thunderbird are you using? What server are you trying to access? Are you talking about gmail? Is it a pop or imap account? What exactly have you done? Are cookies enabled and do you see any google cookies in the 'show cookies' list? Have you made a cookie exception for https://accounts.google.com ? If no then add as an exception and set to 'allow' Do you run a localhost server eg: Apache or similair? if yes then switch it off. You can switch it back on once oauth token is set up. Note: this may be auto installed on some linus systems. What server settings are you using ? Check Thunderbird is not being blocked by the Firewall. Exit Thunderbird. Access Firewall: Is Thunderbird set up as an allowed program in the 'Firewall' ? If no then add it. If yes, it is possible the computer thinks the latest version is somehow different from previous version - it is confused. So - block Thunderbird, ok it and then access Firewall again and set to allow and ok it.