Use of afp:// and vnc:// to dvrdns

Now that things are woking pretty well between Leopard machines, I just checked use of the above for file-sharing and screen-sharing access. The former works perfectly on Safari, but not Firefox - a security issue? The latter works fine both on Firefox and Safari.. one is presented with a screen-sharing window showing the Bonjour machines available, and the Finder window for afp:// - great!