You need to give more information as there is no Thunderbird Account. Perhaps you meant Mozilla Account (formerly called Firefox Account until Nov 1, 2023) which is used for a number of Mozilla services including this support.mozilla.org site and the Thunderbird email client does not make use of the Mozilla Account system. https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-account#w_what-services-can-i-use-with-a-mozilla-account If you have not logged into a Mozilla Account for two or more years you may get notified of account being deleted at a set date unless you login before then. https://support.mozilla.org/en-US/kb/mozilla-account-deletion-inactivity