@nprofile1q... Gmail should be using OAuth to connect, and we have an article on dealing with Gmail authorization issues here https://support.mozilla.org/en-US/kb/thunderbird-and-gmail#w_updating-a-gmail-account-to-use-oauth and here: https://support.mozilla.org/en-US/kb/automatic-conversion-google-mail-accounts-oauth20 - let us know if you still need help after trying the advice here, or open a question in Mozilla Support for our community!