Can't tell which cables are for USB and Firewire?

I'm building a computer using an XCLIO Godspeed Two Advanced Fully Black Finish 0.5 mm SECC / ABS Plastic ATX Mid Tower Computer Case. The cables aren't labeled and I can't tell which cable is for USB and which is for Firewire. I've heard that mixing the two can destroy your motherboard and that they have identical prongs. the manual does not specify which is which either so I don't know what to do.