their is no "USB 3 >USB 2 adapter cable". It's simply a usb 3.0 cable and one end is the same as usb 2.0 (and backward compatible). No idea about the thunderbolt > firewire thing but those both seem VERY expensive for a 3tb drive. I bought a 4tb Hitachi usb 3.0 for $150.
Remember there are now only TWO hard drive manufacturers in the world. Seagate and Western Digital. Lacie simply makes the enclosure and puts a drive in it. Even if it's a "Hitachi" it's a wd, if it's a "Samsung" it's a seagate etc, etc.