That is true if you add it to your session the firewall wont be started until after x. Have you tried:
sudo /sbin/firestarter

in your rc.local?

To the best of my knowledge, the firewall rules get loaded at boot. Firestarter and Guarddog are just graphical interfaces for setting up firewall rules, they aren't the actual firewall.

Yes, I tried sudo /sbin/firestarter in rc.local after adding the required rights in groups.
As said before: ports were closed acc. Shields up after boot.
Ports were stealth after sudo firestarter.
Seems to me that that the firewall-rules are not implemented fully during boot.

If you enter "firestarter -h" you will get all the parameter options.

firestarter -s

starts firestarter but without the GUI.

It just brings the message "Firewall started"

I have put the command in /etc/rc.d/rc.local

It works fine - my firewall starts at boot.