OK, I see your problem. The Firebirdz set is a set of fits for hair made by other people. You would need to obtain the actual hair products to get the fits to work. 

http://www.runtimedna.com/mod/bcs/index.php?ViewProduct=1966&TopID=124211
If you look at the store promo you will see that some items have to be bought. This means the hairs listed under RDNA, DAZ, and Rendo.

But some are free, so you need to go to those sites, download and install those hairs. Then the fits for those hairs will work.

Koz hair, the link to the download page is on the right side of the front page.
http://www.digitalbabes2.com/

Studio Maya
http://www.3digitalcrafts.net/studiomaya/1download/wig1/wig1.html

Sumere and Moko hair
http://digitalbabes2.com/~yamato/Xinxin.html