Well there is a setting on the forum but it's set in the server side not from the ACP menu. you can set the time for the cookie. ie 3600 would be 60 min. I assume it could be set for 0 or something but I need to touch base with Thee on this.
Some things he modified for the sake of security so I obviously have to run this past him. You can control how people log in based on IP, or login name for example. This is not a firefox issue or nix in general. It is controlled by the server running the PHP3 software. I have auto logins for some sites I frequent on Nix and windows that work just fine. As you all know time is a precious commodity for him but I promise I will telephone him and work on this with him soon as possible.