So let me get this straight... you want it to save passwords for you, but not let anybody else see them, but you don't want to have to identify yourself to Firefox? How would that work? If you just want to prevent them from viewing the passwords directly in password manager, that's useless, as they can just go to the site corresponding to the password they want to steal and use one line of javascript in the URL bar to reveal it. Saved passwords are inherently insecure unless they're encrypted with a password you have to enter each time.
From the Anandtech Forums front page, type in your password (don't hit enter), put this in your URL bar:
javascript:alert(document.getElementsByTagName("input").item(2).value);
hit enter, and there's your password.