There is provided a flash suppressor for use with a firearm to attenuate muzzle flash. The flash suppressor can be used in conjunction with attachments, and provides mounting and alignment means therefore. In an embodiment, the flash suppressor comprises: a generally cylindrical body having a longitudinal axis, a muzzle end, and an exit end; a passage extending through the body and along the longitudinal axis; and a set of apertures. The passage includes: a mount portion for mounting the flash suppressor to the firearm muzzle; a transition portion; an intermediate portion; and a truncated conical portion having a diameter that increases toward the exit end. The transition portion joins the mount portion and the intermediate portion, and the intermediate portion joins the transition portion and the truncated conical portion. The apertures extend through the body of the flash suppressor and into the truncated conical portion, and channel propellant gases.