Choose Tools -> Developer Tools > Error Console, paste the expression: 

  and press the Evaluate button. That will open a dialog asking you if you want to reset your password. If Evaluate is not seen, press enter key. When prompted, press the Reset button. 

Thunderbird does not keep a copy of the Master (Primary) password. If you have forgotten it, the following steps should work. All account passwords will then need to be reentered. Choose Tools -> Developer Tools > Error Console, paste the expression: '' openDialog("chrome://pippki/content/resetpassword.xhtml") '' and press the Evaluate button. That will open a dialog asking you if you want to reset your password. If Evaluate is not seen, press enter key. When prompted, press the Reset button. https://support.mozilla.org/en-US/kb/protect-your-thunderbird-passwords-primary-password#w_resetting-your-primary-password-if-you-have-forgotten-it

Si vous n'avez pas bien communiquer en anglais, s'il vous plaît utiliser geckozone - http://forums.mozfr.org/viewforum.php?f=4