Firebomb

From Halo - Wiki on Neoseeker

Incinerating Grenades
Spartan Throwing Fire Grenade

The Firebomb is one of the many new weapons featured in the Halo 3 installment of the series. Like the name imposes, this type of grenade explodes with fire, causing massive damage to anyone in the way of it's blast radius. The Firebomb grenade has been been banned from online matchmaking as it is massively overpowered, with it's splash-damage around the point of impact, as well as cutting of areas.