Even without draining abilities, I think Firelord would win. I don't know too much about him but can't he destroy planets easily? For Superman it often seems to take a lot of effort to destroy a planet or a moon.
Depends really, Firelord has the ability to drain and has more then enough firepower to take Clark down. However baring that Clark wins here, Thor beat Firelord so Clark should at least have a chance if the fight goes physical, because firelord is highly outclassed In that area