Are you talking about the master password? In that case, you could try the following: https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password#w_reset-your-primary-password-if-you-have-forgotten-it

Ronald, It appears that you did mark the response as "helpful" or solved the problem. If you were to more information here, which might be able to help. 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, some 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 If you solved this, posting your results might help someone else.