most cases have firewire connectors on them . Mine has one on the front panel , and the motherboard has firewire header pins that its connected to.
But 5 years ago if you needed firewire the only way to add it was pci card .I have never used it , but some cameras nd video recorders used in when USB was slower. If you dont use it dont worry about it . Leave the case uncluttered and the air flow will be better
It's a good place to put PCI cooling fans. For everything else use PCI Express if you can. I have an ancient PCI sound card which I kept moving to my new systems. One day I took it out and suddenly I can overclock much better and my system doesn't crash anymore. You'd think I would take my own advice. Did creative ever fix the EAX issues in Vista? I heard that their drivers don't use the hardware but run a software wrapper instead. That made me mad. I have a $100 space heater now.