If desperate to try a Firewire to USB converter.... I know of only one that was commonly available, namely the Pinnacle Moviebox that is pebble shaped, not the later square shaped model. It could wrap Firewire data in packets that were sent over USB2. The PC has a driver installed that fools software into thinking the data is coming from a Firewire interface rather than a USB port. This may or may not work with FLIR software as I know such can be fussy !
The unit it worked for Camcorder DV data transfer, but with very mixed user experiences. It worked on some computers, but not others due to differing USB port chip sets plus driver incompatibilities and it could be hard to get working on more modern laptops. These units sell for silly expensive prices on eBay, so think carefully before spending your money. For the same or less money you can buy a good used i7 laptop from HP that has either an integral IEEE-1394 port, or an Extresscard slot to add one.
The Moviebox went obsolete some time ago and Firewire is now considered a legacy interface by many. There is no money in producing such a converter again and the risks of incompatibility make it a poor buy unless very cheap. The Moviebox could be purchased for $100 when released. They are now being sold 'new' on eBay at around $170 due to rarity. Used units sell for around half that price.
I cannot recommend the converter route as it carries high risk of failure and makes little economic sense with so many cheap Firewire equipped used laptops around these days. Some people actually had to buy another laptop that was compatible with the Moviebox ! Pure madness when laptops were still available with a IEEE-1394 port built in. That being said, some people bought the Moveiebix for analogue video capture. The DV to USB converter was just an added feature that many did not even use.
Fraser