[Bozos of Bones]

No, you only need to input your firefox master password when accessing a site that prompts for your password. Meaning, if I were to log out of IW now, I'd be brought back to the log-in screen and the master password prompt would pop up, asking me for my password. If I don't write it in, nothing happens, if I do, the log-in and password fields are filled automatically by Firefox an I can just press enter. It's a very nice feature.