iPod safe to charge a usb ipod with a firewire charger?

well the title pretty much sums it up, i got a griffin powerpod for the car but only when i got it i found out that it s a firewire one not a usb one, is this going to be a problem? i havent plugged it in im scared it ll burn it or something...anyone has an idea.? my guess is i shouldn't but i wnated to know whta u guys think