i dunno if this really goes w/o saying or what, but i haven't seen it mentioned. when my guild was first trying the fight, greater fire resist pots helped a ton. we'd usually give 3 to each priest and 1 to the dps. dps would save their pots for when their priests died, so they'd have a short extra bit of time to dps. priests would pop their pots as a means of avoiding interruption, so they could get out extra spot heals on groups whose priests had already died
as one of the guides said, we would have shaman strictly healing the mt. they were only in their groups for fr totem. since we only ever had 1 or 2 druids per raid, they would basically just drop HoT's on the dps. they didn't focus much on mt's like the guides said. priests obviously group healed and spot healed.
it's been a few months since i stopped playing, so i don't know if they still use so many fr pots, though i doubt it. as you learn the fight, it gets a lot easier, and like ppl said, the mt transitions are the most important part, but in learning the fight, the extra padding from having fr pots helped out. at least as a priest, i was able to pay more attention to groups other than my own to keep up dps when other priests got ba'd, which added to overall dps and everything