Death From Above

only 3 of the firlelord are available to be bombed each day.. dont waste 30 minutes like i did trying to figure out why the hell i couldnt find the rest even though i was using /target commands

Six Firelords that appear during this bombing daily quest Fire in the Skies.
When you bomb all 6, you will get the achievement Death From Above.

To bomb these guys, you'll be on a fire hawk (provided seige type vehicle next to the quest giver) with 3 options: Flame Seed, Flame Burst, and Return to the Furnace.

They regen HP quickly, so to defeat them you'll need a group effort (though they may just get to 1 hp and not die =-/ )
You do not need to kill them, some people just get trigger happy, and it does count if you bomb them when they're "tagged" or gray/grey nameplate.

The Six Firelords:

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• Ragepyre
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• Ragepyre is off to the right as you leave the cinderweb area. He's atop a small barren hill. (In Firelands there's surgers here.)
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• Flashfire
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• "Flashfire is semi-hidden in the hills on the right as you leave Beth'Tilac's area via the ramp." (Thanks Toroq!)
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• Heatflayer
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• Heatflayer is in the cinderweb area (Beth'tilac's lair) on the western most part. He's slightly smaller than the other Firelords. (Thanks battierpeeler!)
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• Blazefury
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• Blazefury is located on the left hand side after you bomb the open area with corehounds, and are headed back up to the cinderweb (Beth'tilac's Lair) area. You may have tried to knock the flamewakers off the ledge here with Flame Burst, just look to the left.
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• Hatespark
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• As you're leaving the cinderweb area (or if you just arrived) and are flying down the ramp, look to the left atop a pillar.
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• Singeslayer
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• "Singeslayer is off to the left as you leave Beth'tilac's area." (Thanks kaytie!)
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It appears that these can change daily, although from looking at builds it may be weekly.
The daily by daily terms can queue twice, though unlikely as these appear to be cycling as intended, meaning you may get a different Firelord every 3-4 days (or depending on how often you do your dailies).
Update: It appears the daily is one of four possible dailies. One day you'll steal an egg doing Peaked Interest, the next day you may bomb away. As far as which Firelord will be there, there may be a cycle for them, but it appears that every other day it will change.

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• "Elementals change at 1:00am pacific 4:00am eastern." (Thanks battierpeeler!)
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The prerequisites to this daily is to obtain 150 Mark of the World Tree, and turn in the quest Druids of the Talon at the Shrine of Aviana.

Upon turning in the quest, you will get some short LolRP, then the NPCs will head off to the Molten Front. As you're leaving there is a quest available from the innkeeper Isara Riverstride called Flight of the Storm Crows which just tells you (if you ignore LolRP) to go to the Molten Front and do dailies.

From here you'll finish your dailies, get your marks, and then a new daily will appear to escort a druid through the flames to the north west. As you escort her, fire nagas will spawn to attack and disrupt her concentration to make you burn. About 5 of these spawn, just kill them off. They have roughly 60-70k hp. When you reach the end, a molten elemental will be standing there and the attack is called. DPS the elemental, and stay out of fire that is put under your feet that explodes shortly afterwards. When the elemental is defeated you'll be sucked in as it explodes and dropped down a shaft. Down here is your first set of new dailies. Finish up down here, and don't forget (if it's your first time) to get the escort quest in the far back of the cave (watch your minimap). When you head back up, simply go to your left around the side of the mountain, and here's where the Druids of the Talon daily hub is located.

Meh, if more time available will edit this for clarification as far as the prerequisites section goes.

Just to note since it confused and frustrated me for quite some time before I figured it out: you just have to bomb the named Firelord, you do not have to kill him. In fact, without extreme coordination between multiple people doing the achieve together killing him would be very much impossible as you can only do ~20-25% of his hp in damage in the time you are in range of him and he evade regens almost instantly.

Hope this saves some people some frustration as it's not exceedingly obvious, esp. if the Firelord for your first bombing run is one of the ones after the "..." when tracking the achievement (update just removes the ellipses marks, very subtle).