Chuckles, Smarter, Halo 3: ODST comes out September 22.
FireFight works like this. There are five waves in each set. There are three sets per round, so that's fifteen waves per round. After every wave, a random skull turns on to increase difficulty, such as tough luck, which makes it so enemies dodge grenades a lot easier, or the other skull, don't know it's name, but it makes it so the only weapon the enemies have are grenades.
And each wave also gets harder because more of the enemy arrives to kill you, first wave might be grunts, second might be grunts and jackals, third might be brutes and grunts, etc.
Your team also has a set of limited shared lives. Your whole team I believe starts with five lives, if your teamate dies, then your lives go down to four. This is why you have to work and stick together. If you have anymore questions, please feel free to ask. Also, you can gain back lives with the events that popup ingame. Ex: A message pops up saying if you get 5,000 points in under one-minute, you get an extra life.
Read my FF! Human-Covenant War: Without The Great Schism. It's an FF based upon how the war would have ended up if there was no Great Schism. There are a lot of twists and there is a lot of action!