Обнаружен любопытный сайт по безопасности, создатель которого разработал пару утилит для восстановления паролей Firefox:

FirePassword:

FirePassword is the tool designed to decrypt the username and password list from firefox signon database. Firefox stores the username and password information for various sites in its database files. FirePassword works on similar line as Firefox's built-in password manager but it can be used as
offline tool to get the username/password information without running the Firefox.

FireMaster:

Firemaster is the Firefox master password recovery tool. If you have forgotten the master password, then using FireMaster you can find out the master password and get back your lost signon information. It uses various methods such as dictionary, hybrid and brute force techniques to recover the master password from the firefox key database file.

Утилиты и исходники доступны на сайте разработчика