That message you see is just the last line of kernel messages before it hangs during boot. Your problem has nothing to do with firewire, which is unsupported (and ignored) hardware.
The easiest way to find the root cause is to do a verbose kernel boot.
Step 1: At the boot> prompt, type "boot -c"
Step 2: At the first UKC> prompt, type "verbose"
Step 3: At the second UKC> prompt, type "quit"
Step 4: See if there are any messages produced
after the firewire probe has ended. This should point to the device causing the hang. It can be disabled at the UKC> prompt if necessary.
For more detail, see the
boot_config(8) man page.