Sounds as though the problem may be based in hardware, so it may be subject to inspection by a professional who may be able to diagnose if the FW port is defective or not.
There are a few 'reset' actions that may not have any bearing on the restoration of Firewire port function, but as a process of elimination, they could be tried anyway. Some of them could affect how software acts on the hardware. If there is a hardware failure contributing to the FireWire, there are repair service facilities who work on these still. A few can resolder logic boards and other detailed repairs, too.
•About NVRAM and PRAM:
•Resetting PowerBook and iBook Power Management Unit (PMU)
Not sure if this will help...
Good luck & happy computing!