That only works in one direction. You can use it to connect FireWire devices to a computer with Thunderbolt, but you can't use it to connect Thunderbolt devices to a computer with FireWire.
Contrast with USB. I can go out and buy a USB storage device brand new off the shelf in 2015, plug it into an iMac from 1998, and it will work. It will be slow but it will work out of the box.
