firewire (FW) was invented by Apple, and it's a trademarked name. So other manufacturers that use it too give it a different name. The official standards name is IEEE1394. Sony calls it iLink.
It has a speed of 400kbps. USB1 has a speed of 12kbps, while USB2 has a speed of 480kbps.
So USB2 is slightly faster now. However, FW is made to connect to one device at a time, and offer maximum speed to that device at all times. USB2 is designed in a totally different way, in that it's made to accept multiple devices into one port (hence you can buy USB hubs). These devices only operate as fast as the slowest device connected to that USB port, and it doesn't always run at maximum speed either.
So often FW is faster, even though on paper USB2 should beat it.
Another small complicated is that there's now a successor to FW. The original, as I say, had a speed of 400kbps. The new one has a speed of 800kbps (I believe this is IEEE1394b). So there's firewire400 and firewire800. If it just says firewire, then it's most likely to be 400 though. Most manufacturers are yet to include 800; Apple have added it on some of their newer computers (the 17" MacBook Pro for instance, but not the 15").