Read from the World of Warcraft client build files.
How Firebird's Spaulders Compares
Who It Suits
Mail is the armor type Evoker, Hunter and Shaman wear. With Agility or Intellect, Firebird's Spaulders suits Beast Mastery, Marksmanship and Survival Hunter; Elemental, Enhancement and Restoration Shaman; Devastation, Preservation and Augmentation Evoker.
Transmog Sets
Firebird's Spaulders is part of the transmog set Regalia of the Firebird (Shaman only). The other 16 pieces:
Built from the World of Warcraft client build files and recorded Auction House snapshots.
Where Firebird's Spaulders Fits
Other Items Named Firebird's Spaulders
3 other items in the current build are also called Firebird's Spaulders. Same-name entries are usually a different rank, faction, quest stage or reward track of the same object.
Blizzard numbers items as they are created, so the named items next to ID 87138 (87133 to 87143) were usually added in the same batch as Firebird's Spaulders: the same quest line, zone, vendor or reward set.