There must have been hundreds of these posts now. Here are a few from your "See Also" list in your topic on the webserver https://support.mozilla.org/yo/questions/1515118 https://support.mozilla.org/yo/questions/1471695 https://support.mozilla.org/yo/questions/1534274 https://support.mozilla.org/en-US/kb/thunderbird-and-gmail All discuss oAuth authentication which is what you are having issues with. I have no idea what your are being asked to authenticate or why. I would guess it is either about an email address, a calendar or a Google address book as those are the things that use oauth on Google.