If using version 68*: Follow exact instructions as found at this link: 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 If using version 78*: Follow same instructions but.... You need to change the last bit of the line you need to copy. Copy and Paste all the following text instead of the text at the link above: openDialog("chrome://pippki/content/resetpassword.xhtml") Please note, As the purpose of a Master Password is to protect stored passwords, when the Master Password is removed/reset it means all stored passwords are removed.