So I was datamining a little, and found the Firelands bosses voice files. The only one who doesn't have a voice is Beth'tilak. So here we go:
Lord Rhyolith:
Aggro: *Grunts* Soft little fleshy things? Here? Nuisances! NUISANCES!
Kill1: Finished!
Kill2: So soft...
Kill3: Squeak little pest
Chunk1: Oww... The pain
Chunk2: *In pain*
Chunk3: Oww, smushy little pests, look what you've done!
Chunk4: Oww, you... you...infuriate me!
Chunk5: Oh you little beasts
Lava1: Burn!
Lava2: Succumb to living flame!
Lava3: My inner fire can never die!
Lava4: Consume!
Lava5: Flesh.... burn!!!!!
Stomp1: Stop now!
Stomp2: I'll crush you under foot
Transform: Eons I have slept undisturbed, now this... Creatures of flesh, now you will burn!
Quest1: Crush! Crush! Crush!
Quest2: Sear their flesh from their tiny frames
Quest3: Shatter their bones!
Quest4: Stomp and burn! STOMP AND BURN!
Death: Broken... *mumbling* broken...
Alysrazor:
Aggro: Hahaha! I serve a new master now, mortals!
Kill1: Burn!
Kill2: For his glory! Muahahahaha!
Spiral1: These skies are mine!
Spiral2: I will burn you from the sky!
Transition1: Fire.....Fire!!....
Transition2: Reborn in flames!
Quest: No! NOO! I didn't betray the dragonflight, we were all betrayed! Ysera was lost in a dream while this whole world came undone!
Death: The light musn't... burn out....
Shannox:
Aggro: Ahahaha! The interlopers! Kill them! Eat them!
FireAttack1: Now you burn!
FireAttack2: Twist in flames, interlopers!
Kill1: Yes! Oh yes!
Kill2: The firelord will be most pleased
Kill3: Now you stay dead!
Kill4: Dog food!
Spawn: Yesss... I smell them too Riplim. Outsiders approach on the Firelord's private ground. Find their trail, find them for me, so that I may dispense punishment!
SpearAttack1: Step off!
SpearAttack2: Back! Stay back!
SpearAttack3: Get away from me! Outsiders!
SpearAttack4: Back, filth!
Quest1: You are marked for death! Go! Flee little one!
Quest2: You are being hunted! Ahaha!
Quest3: Time to run! Shannox comes!
Quest4: The realm of fire will consume you!
DogAttack1: Go for the throat!
DogAttack2: Tear them down!
DogAttack3: *whistles* Kill!
DogAttack4: Sic 'em
DogAttack5: Fetch your supper! Ahahaha!
DogDeath1: Riplim! No! Nooooo! Ohhhh you terrible little beasts! I'll cut you!
DogDeath2: Ohhh you murderers! Why? Why would you kill such a noble animal!?
Death: Ohhh.. the pain! Lord of fire it hurts!
Baleroc:
Aggro: You are forbidden from my master's domain, mortals!
Event1: I enact my master's will, I am he who barres the gate!
Event2: Foolish mortals! Hurry yourselves into your own demise!
Event3: By the Firelord's command, you too shall perish!
Kill1: Learn to grovel
Kill2: You have been judged!
Kill3: Your flesh is forfeit to the fires of this realm!
Kill4: Behold your weakness
Kill5: None shall pass!
Quest1: The master will see you all consumed!
Quest2: Be swallowed by a sea of flame!
Quest3: Burn beneath my molten fury!
Quest4: None may enter the master's domain!
Death: Mortal filth... The master's keep is forbidden...
Majordomo Fandral Staghelm:
Aggro: Very well, witness the raw power of my new lord.
AlysrazorIntro1: What have we here? Visitors to our kingdom, the Firelands?
AlysrazorIntro2: You mortals may remember Alysra, who spirited me to freedom in Mount Hyjal, she too has been reborn. Born of flame!
AlysrazorIntro3: I wish I could watch and reduce your pitiful band to cinders, but I am needed elsewhere. Farewell.
FirebirdTransform: Blaze of glory!
GateIntro1: Well well... I admire your tenacity, Baleroc stood guard for the keep for a thousand mortal lifetimes.
GateIntro2: But none may enter the Firelord's abode
GateIntro3: Beg for mercy now, and I may yet allow you to live. Well heroes, what is your answer?
Kill1: Hahaha, burn!
Kill2: Nothing but ash!
Kill3: Soon all of Azeroth will burn!
Kill4: Hahahaha! So much power!
Kill5: You stood in the fire!
ScorpionTransform: The master's power takes on many forms!
TigerTransform: Behold the rage of the Firelands!
Death: My studies... have only just... begun.
Ragnaros:
Aggro: Mortal insects! You dare trespass into my domain? Your arrogance will be purged in living flame!
Adds1: Come forth my servants, defend your master!
Adds2: Minions of fire, purge the outsiders!
Adds3: Denizens of flame, come to me!
Adds4: Arise servants of fire, consume their flesh!
HammerDrop1: You will be crushed!
HammerDrop2: Die!
HammerDrop3: Your judgement has come!
HammerPickup1: Enough! I will finish this!
HammerPickup2: Fall to your knees mortals! This ends now!
HammerPickup3: Sulfuras will be your end!
Kill1: Die insect!
Kill2: Pathetic!
Kill3: This is my realm!
Purge: By fire be purged!
Quest1: Begone from my realm insects!
Quest2: I will see you all burn!
Quest3: Consumed by flame!
Quest4: The realm of fire will consume you!
Heroic1: Too soon...
Heroic2: Bah, outsiders, this is not your realm!
Heroic3: When I finish this, your pathetic mortal world will burn with my vengeance!
DeathNormal: Too soon, you have come too soon!
DeathHeroic: No! Nooo! This was to be my hour of triumph!
Edit: Video is up!
Thats it, all Firelands quotes from all the bosses who have them. As mentioned I skipped a little of Fandrals quest quotes, might add them later.