Join the AMA (Ask Me Anything) with the Firefox leadership team to celebrate Firefox 20th anniversary and discuss Firefox’s future on Mozilla Connect. Mark your calendar on Thursday, November 14, 18:00 - 20:00 UTC!
Then reset it.
https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-master-password#w_removing-your-master-password-if-the-master-password-has-been-forgotten
