[Osiris]

While the Master Password in Firefox is a useful security addition it can soon become a burden if you lost the password that you entered there. There is no way of simply looking into a file and copying your master password from it, would not make much sense at all to add a master password that could be looked up in a file.
The user who has forgotten his master password has basically only the choice to reset the password which unfortunately means that all login details will be lost in the process. The only other way that could bring a result would be a brute force attack. The success of the latter method depends on the password that you have chosen during setup of the master password.
Brute Force will most likely succeed if the master password consists of a existing word, words or names. It will not succeed in reasonable time if the user entered a random password with letters and numbers.
Reseting the Master Password in Firefox:
Open Firefox and paste the following line into the address bar:
chrome://pippki/content/resetpassword.xul
A text will appear saying that if you reset your master password all login details including usernames, passwords and websites will be lost. If you click on Reset the master password is reset which means that you can enter a new one. Cancel would be the other option.
Brute Force the Master Password in Firefox:
You can use a software called FireMaster to try and use the Brute Force method to regain your Master Password.

* FireMaster generates passwords on the fly through various methods.
* Then it computes the hash of the password using known algorithm.
* Next this password hash is used to decrypt the encrypted data for known plain text (i.e. “password-check”).
* Now if the decrypted string matches with the known plain text (i.e. “password-check”) then the generated password is the master password.

I would only use the brute force method if you are nearly certain that you used a word or word combination. A password like ‘X23n52fF:tht0_ete%v5′ would take ages to reveal.
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FireMaster