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.
http://firefox.phpmagazine.net/upload/2006/10/firemaster-thumb.jpg
Firefox uses master password to protect the stored signon credentials. Now if you have set this master password and forgotten , that means you have also lost the authentication details for various websites which has been stored in firefox signon database. So far there was no way to recover these credentials once you have lost the master password.
Download Firemaster [Binary] or [Sources], Gecko SDK required to build from sources.