What devices is the iPod to Firewire 400 adapter meant for, and for what purpose?
This is a Firewire 400 to iPod 30-pin adapter.

If you have an older iPod, you may be able to sync and/or charge it via Firewire. This site has an exhaustive list: Which iPods can sync and charge via USB? Which iPods can sync and charge via Firewire?

It looks like some models supported Firewire charging as recently as 2009, but no models since 2006 or so have the ability to sync media over Firewire.