Surfer and Firelord have worked together before, though not effectively, but if they had to take down the two gods, would they have a chance? Let's say Thor and Loki are working together for this battle.
Thor and Loki don't work effectively together either, but they would take it assuming Loki didn't try to kill his partner. Firelord is seriously overrated anyway and I think Surfer would have problems with Loki. I assume you mean Classic Thor otherwise it's not even a contest.
Thor and Loki have worked well at times both in continuity (as they battled with Odin as a threesome against an empowered Surtur w/Twiligh, and in the wars of Asgards past).
Thor owns either Herald, Loki would destroy Firelord and could match the Surfer.
Thor and Loki ftw, 10/10.
__________________ Among the tales of sorrow and of ruin that come down to us from the darkness of those days there are yet some in which amid weeping there is joy and under the shadow of death light that endures.
J.R.R. Tolkien, "Of Beren and Luthien" from the Silmarilion