Firebird is a floorless roller coaster located at Six Flags America in Prince George's County, Maryland. The roller coaster had originally debuted in 1990 as a stand-up roller coaster named Iron Wolf at Six Flags Great America. It was later relocated to Six Flags America in 2012 and renamed Apocalypse, under which it operated until 2018.

A stand-up roller coaster is a roller coaster where passengers aboard a train stand throughout the course of the ride. The first manufacturer to employ the format was TOGO, a Japanese company that converted two traditional roller coasters in 1982 to stand-up configurations. Arrow Dynamics followed suit in the United States the following year with their own conversion. The first roller coaster designed from the ground up as a stand-up coaster was King Cobra, built by TOGO, which opened at Kings Island in 1984. Intamin and Bolliger & Mabillard (B&M) have also designed stand-up models beginning in the 1990s, with the latest opening in 2023 as Pipeline: The Surf Coaster in SeaWorld Orlando.