How to get green fire for your warlock
I guess everyone knows by now that 5.2 patch will finally bring the warlock green fire quest. If you didn't know about it, well, you do now.This quest is a warlock class specific quest and if you decide to complete it, you'll learn a new passive skill, and that spell will change your fire spells. That's right, your fire spells are going to be green now.
How do you start that quest
To start the green-fire quest, you'll have to be lucky basically. Every mob from the Isle of the Thunder, including the rare ones, has a chance of dropping the Sealed Tome of the Lost Legion. I don't know the actual chances of that Tome to drop, but if you put your mind into it it will drop eventually.
Basically this is the hardest part, to actually get that Sealed Tome, after that it's all about patience.
The quest chain
Now you are the happy owner of the The Codex of Xerrath, but you can't read it. Here is where your minions will help you. Try summoning one and ask them what they know about that Codex.
You'll be sent to your capital city, Orgrimmar or Stormwind, to seek help from your Warlock Trainer. He will give you a Journal and ask you to search for some long lost Soulstones.
Switch the green fire on and off
It was told already that we will be able to switch the fel fire on and off and I'm here to tell you how you can do that.
After completing the scenario, the Kanrethad demon, that you just defeated, was banished and held next to the Altar of Damnation in Shadowmoon Valley. There you can unlearn your passive skill.
Conclusion
It's pretty nice to see that the class quests coming back into the game. I also like the way you are starting the quest. I don't think you'd like to see every warlock with fel fire now.
Unfortunately the story inside Black Temple seems to be unfinished now, on PTR, and I feel like I ditched Akama in there after he trusted me.
I really hope I'll see more class quests in future patches. It's really nice to have something else to do with every alt of yours.