I am a newbie to Linux, but I guess I at least know what your issue is.
It is not the "first boot" but the "firstboot" service that is executed during startup. I had this problem, too. I pressed "I" during boot to enter interactive startup. I said "y" to the startup question for all services, EXCEPT for firstboot. That allowed me to boot into the GUI.
Then I opened a terminal and started "firstboot" manually by typing it. After completing firstboot manually, it is also removed from the system startup services.
I experienced this with Red Hat 9 on a Compaq Armada E500 notebook.