We found 2 Reddit comments about Fire Warrior (Warhammer 40,000). Here are the top ones, ranked by their Reddit score.
Fire Warrior is still available! https://www.amazon.com/dp/B01MQWBGM3/ref=cm_sw_em_r_mt_dp_U_w6WvDbS59R6WQ
The first book I bought was an E book full of other books.
The Tau Empire A Legends of the Dark Millennium book
Shadowsun: The Last of Kiru's Line
A Sanctuary of Wyrms
Fire and Ice
The Patient Hunter
This book is from the perspective of a Rogue Trader and the first crusade attacking the Tau Empire.
Rogue Trader Omnibus
This book is about an Imperial Guard regiment fighting Gue'vesa and Tau forces.
Fire Warrior Is about an individual fire warrior absolutely wrecking imperial forces on his own. It gives a lot of interesting views on imperial culture from the perspective of the fire caste.
I would absolutely buy the first book listed again, it's 10 stories. Some of them are pretty short but it's neat how you hear about some of the characters again in other books.