We have a bugreport in debian, http://bugs.debian.org/737142, stating that PC-BSD does not work with seabios-1.7.4 anymore.
I digged in, and found out that it fails only with -vga std (cirrus works fine). So I bisected the issue - only changing vgabios-stdvga.bin, and found this:
9332f9b172dd59253365a83b5f1c0e40c5f6f66d is the first bad commit commit 9332f9b172dd59253365a83b5f1c0e40c5f6f66d Author: Kevin O'Connor kevin@koconnor.net Date: Sat Nov 30 12:52:44 2013 -0500
vgabios: Work around lack of support for "calll" in x86emu emulation.
Replace 32 bit call instructions with 16 bit call instructions in the vgabios to workaround problems in old versions of x86emu. This change allows fc13 and fc14 to boot. (Other x86emu emulation bugs still prevent fc11 and fc12 from booting.)
I'm not sure what is better - to have semi-working FC13 or non-working PC-BSD ;)
Seriously, I don't really have any expirience in this area to understand what's going on. Note that PC-BSD fails clearly in some VGA-related code, and this is trivially reproducible.
Thanks,
/mjt