Opening a topic should have the browser go to the first unread post in a topic if there are new replies, or the first post if there are none. I don't think there is a forum option to change that. I don't know if a specific browser can be set to ignore the '#UNREAD' at the end of a topic URL, but hitting the Home button with bring the focus back to the top (though that could get annoying if you always want to start at the top of a forum topic).
