Master Password Timeout is a Mozilla Firefox extension which locks the master security device after a predefined period of inactivity (timeout). By default, 300 secs (5 min) of inactivity will lock the master security device, but this value can be adjusted in the extension manager options window. When the master security device is locked, the master password must be entered to gain access to saved passwords.
The latest version of Master Password Timeout can be obtained here.
If you found this extension useful (or useless) please drop me a line to share your thoughts and suggestions. If you can help with any of the above bugs/issues make sure you let me know! My email is below.