Firefight

"Welcome to the last day of the rest of your life."

Firefight is a lot like Horde Mode, only it's Horde Mode on fire, going 130 miles per hour through a hospital zone, being chased by helicopters and ninjas. And, the ninjas are all on fire, too.

You and up to at least three Battle Bros can get together and fight waves upon waves of the Covenant onslaught. You keep going until you die.

Origins
Firefight was a game mode that was going to be implemented in Halo 3 but ended up being cut to meet deadlines. It made its triumphant return in the expansion Halo: ODST, and was met with much praise and was one of the major selling points of the game. It is now returning in Reach, but with the customization of all other gametypes.

How it works
Firefight in Reach will follow the same formula that it did in ODST. Five waves in a round, three rounds to a set, and as many sets as you can take before you run out of lives. These lives are shared between all players. A standard game of firefight matchmaking will last for a single set.

Firefight Voices
In Halo: Reach instead of selecting a character to play as, you use the same Spartan universally throughout Reach. Selecting a Firefight Voice in the armory will make your character talk shit in the voice selected. Confirmed voices include Noble 6, Emile, Carter, Kat, Jun, Jorge, John-117 (Master Chief), Cortana, Buck Reynolds, Avery Johnson, and Pete Stacker.

Trivia

 * In one of Bungie's Weekly Updates, they posted all of the options that you can customize in Firefight. protip: it's a fucking lot.
 * The NT1 Generator Defense playlist in the Beta was actually a test of matchmade firefight. This was already leaked by those who had hacked the Beta and found that the map was constantly attempting to load waves of AI that didn't exist as well as strings confirming the presense of firefight.
 * The NT1 Generator Defense has been confirmed as an objective based firefight gametype.