See https://support.mozilla.org/en-US/kb/password-manager-remember-delete-change-tb and https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password Be aware if Thunderbird just started asking for your password it is unlikely it "forgot" but that connection to the sever using the password is has was rejected. It may have deleted the password after multiple failed attempts (and clicking cancel on the request for a password), but I really don't recall a time when it actually "forgot". That would require a rather serious bug. Also note that most requests for a password mean you have a security product/antivirus that has messed up post an update resulting in no mail. See https://support.mozilla.org/en-US/kb/cannot-receive-messages

Deborah, is your problem solved?