Firefight is not to different from zombie in COD. The main difference is that you start in a small area and unlock new parts of the map as you progress through the waves. Also you upgrade your guns along the way. I think firefight (or Floodfight, win) you should start out with maybe an assault rifle and a pistol. As you progress through waves you get better and stronger weapons with the ordinance drop pods. That way you don't get the sniper or rocket launcher round one.
Also the ability for firefight to be like invasion where you also have objectives to complete to unlock other parts of the level as well.