On a PC, the USB port is "guaranteed" to work. The firewire port is not "guaranteed". On the Mac it's the opposite: the firewire port is "guaranteed", and the USB port is not.
I have had it work to transfer files using firewire on the PC, but it definitely works better with the USB port.
Note: this has nothing to do with firewire streaming; that always happens exclusively through the firewire of course. We're talking about using the camera as an external P2 card reader on a computer.
