1. Even in sudo, it's easy to find the logged-in user. Just look at $SUDO_USER (or, from a terminal type "sudo env" to discover sudo's environment). See also $SUDO_UID and $SUDO_GID.
2. Please don't switch to the policy method. It's a scourge since it ignores the settings in /etc/sudoers without providing an alternative. Thus, the user has no control over the system any longer. Too many apps are converting to that method. Please, let's not have another. Sudo works very well.
3. GDM2Setup shouldn't unconditionally launch Firefox. My default browser is Chrome, and I'm using a netbook with limited RAM. Starting a Firefox instance over-stresses my system. Just launch the default browser (such as by calling gnome-open).
This is a side effect of using the older "sudo" method of runing the application and needs to be replaced with the newer "policy" method.
Thank you for this report.