Kite him to vaels room...
No really :), we do it every week and the positioning shown below works great for us. Only thing needed is 1x speed pot for MT for the pull.
Red = firemaw's final position
Yellow = MT
Darker Blue = OT
Lighter Blue = Healers in RG's room
The DPS (and a few healers) sit in vaels room behind one of the colums during the pull. The OT's and the MT/OT healers chill in there spots. The MT goes into the broodlords gate, when firemaw is visible on his patrol, the MT chugs the speed pot, aggros firemaw and head for the supression room. Here you just jump off onto the 2nd platform. This gives you plenty of time for the MT to reach his position as firemaw must path down and can't "jump" down through the supression room.
The one IMPORTANT thing to do in the pull however is DONT DO ANYTHING. No buffing, no stance changing, no eating/drinking/pots/totems/innerfire/ANYTHING. With the entire zone in combat and no aggro from the MT to firemaw, the slightest thing will make firemaw go to the raid and pwn them instead of following the MT to the tunnel between vaels room and RG's room. Just don't do ANYTHING and it works fine though.
The LoS here is idiot proof. You really just can't screw it up. Healers for the MT aren't ever in LoS, Healers for OT aren't either. DPS just runs out of LoS into vael's room to bandage.
General tips for firemaw:
315 FR on your MT and OT(we use 2 OT incase of taunt resist).
High FR on your raid EXCEPT your healers. Healers should be in full regen as they will never get hit by the fire debuff.
When you get the shadowflame warning, have your quickest reactionable priest PW:Shield the MT to absorb 1k dmg. Saves your tanks from death if they happen to not be topped off when a SF comes.
Firemaw has a "thrash" ability (alot like windfury) and that combined with regular melee, the fire damage, and shadow flame: he can put out some serious damage to your tanks. This fights all about healing here.
*edit*
Make sure your healers dont heal the MT when he arrives at his position to tank. Have the MT bandage or else firemaw will go pwn your healers instead of the MT. Also your healers need to be on their toes to heal the MT the second he starts taking damage. Tell them to angle their camera so they can see down the hallway while off to the side in RG's room.