Hmm, I'm afraid I don't know much about Fire Girl yet either, other than the fact that it's from the guy who wrote
Room of the April Witch/one of the guys behind Girl's Work, Meteo Hoshizora. Taking a quick look around myself, there doesn't seem to be a whole lot of information either, other than some information about the main characters and the basic premise, likely due to a lack of a translation.
There's a chance that someone around will know more than me though.
And while you've likely found it for yourself already, here's the official site at least:
http://www.typemoon.com/products/tmbooks/firegirl/
