This quest is locked until you complete the introduction Dragonslayer quests, which are in turn unlocked by a breadcrumb quest from Jabarik inFortune's Shore. You must be 50 to get the breadcrumb quest.
Once unlocked, you can turn them in a stack at a time for Dragonslayer Covenant rep. You can save these up in stacks then just turn in the quest, get it again, turn it in again, and so on. If you are not 50 yet but can hunt these mobs, you can store up the Firebrands for when you can turn them in. You do not have to have the quest to get the drops.