No, firefight was not introduced until Halo ODST which was made after Halo 3. Only Halo ODST and Reach currently support it. Halo 4 will have a new game type called Spartan Ops which is similar.
yes it does
you can play as Sgt. Johnson in fire fight mode.
yes fire fight mode is addicting! somwhat dissapointing
You have to at least have a memory unit with a live account
forge probably not but it will come with 3 new maps for halo 3 and you play fire fight and the campaign in a bigger version of nomindbasa from halo 2
We aren't sure yet.
There WILL NEVER be a Halo 4. Halo 3 is the end of the story. ''Finnish the Fight'' and all that.
Finish the Fight
Yes, but you need to do it over xbox live.
No.
basiccly no achievements, but it will say you finished the fight
no Gravemind was the leader of the flood and that virus. The elites in halo 3 join the UNSC marines as they fight the covenant and the flood