Napalm grenade

Historically, Napalm is a mixture of chemicals which, when mixed with gasoline, makes a sticky incendiary gel. Developed by the U.S. in World War II by a team of Harvard chemists led by Louis Fieser, its name is a combination of its original ingredients names:
 * aluminum salts of naphthenic and palmitic acids = Napalm

The name has since evolved from just the gasoline and Napalm gel to mean any substance that causes intense fires upon ignition.

It the Halo Universe the Napalm Grenade was used by UNSC forces in the Halo Novels. It could be in Halo 3 because a "firebomb grenade" was found in hex.