How to find the firefight option

This might be a silly question, but where do you find the Firefight Option in the game? I only have 4 Menu options to choose from. Campaign, Halo:REach Anniversary Multiplayer, Halo Waypoint and Extras. None of them lead me to the Firefight option. Thanks.

Go to the Halo Reach Anniversay Multiplayer section.

Then in Matchmaking, select Firefight.