My kickstart script explicitly disables firstboot. It contains a line reading `firstboot --disable`. Incidentally, the documentation at http://fedoraproject.org/wiki/Anaconda/Kickstart states that firstboot should be disabled by default anyway. The machine was installed from rawhide last Friday.
What does rpm -q firstboot tell you the version number is?
I've reinstalled the machine a few times, and I've had some network problems in the process. To make a long story short, I'm having trouble reproducing the problem. I'll close the ticket for now, but I'll reopen it if I can get it to happen again. Thanks!