I recenlty forgot my firefox Master password and searched for process to recover/reset the master password and found this solution to reset it.

Note: Upon resetting, you will lose all the stored information in the Password Manager, as this is a built-in security feature to prevent people from simply resetting your Master Password to gain access to your passwords.

In the firefox Addressbar
Type

chrome://pippki/content/resetpassword.xul

press the “Enter” key and click “Reset”.

Hope this helps someone.

Referenced From : ‘http://kb.mozillazine.org/Master_password