Let's stick in 2d8 for now, we can always change it later.
Come to think of it, will we be using 5 ft. for the range like a Salamander or make it 10 ft. because this firelord's a big lad?
Did a bit of tweaking to get the following:
Body of Smokeless Flame #2. A creature that touches the efreeti firelord or hits it with a melee attack while within 5 or 10 feet of it takes 9 (2d8) fire damage. In addition, whenever a creature or object ends its turn within 5 or 10 feet of the firelord, that target takes 9 (2d8) fire damage and ignites. A burning target takes 5 (1d10) fire damage at the start of each of its turns. A creature can use an action to douse the fire, ending the effect.
EDIT: a
Balor Demon is also Huge and its Fire Aura also has a 5 foot effect so I'm OK leaving it at 5 feet and it does make Reach weapons useful for the firelord's Medium sized opponents.
Fire Aura. At the start of each of the balor's turns, each creature within 5 feet of it takes 10 (3d6) fire damage, and flammable objects in the aura that aren't being worn or carried ignite. A creature that touches the balor or hits it with a melee attack while within 5 feet of it takes 10 (3d6) fire damage.
Hmm…
Actually, perhaps we should use some of that ability's wording for the Firelord…
Body of Smokeless Flame #3. At the start of each of the efreeti firelord's turns, each creature within 5 feet of it takes 9 (2d8) fire damage, and flammable objects within that distance that aren't being worn or carried ignite. A creature or flammable object that touches the firelord or hits it with a melee attack while within 5 feet of it takes 9 (2d8) fire damage and catches fire; until someone takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.
I like the "catches fire; until someone takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns" wording over the previous "" as it's clunkier, so I'll revise #2 to:
Body of Smokeless Flame #2a. A creature or flammable object that touches the efreeti firelord or hits it with a melee attack while within 5 feet of it takes 9 (2d8) fire damage. In addition, whenever a creature or flammable object ends its turn within 5 feet of the firelord, that target takes 9 (2d8) fire damage and catches fire; until someone takes an action to douse the fire, the target takes 5 (1d10) fire damage at the start of each of its turns.
Of the above I like
#2a the best so far.