Players need to complete daily quests available at Sanctuary of Malorne in Mount Hyjal for approximately 5 days (25 Mark of the World Tree) in order to gain access to the Firelands portal sitting atop the peak in front of Sanctuary of Malorne.
Once inside, Malfurion Stormrage and the Guardians of Hyjal faction fight against Firelands forces. Upon defeat, Malfurion Stormrage walks toward a cave where you will now find a troll named Zen’Vorka (Horde) or Captain Irontree (Alliance). These vendors sell some interesting items. Few of them, but useful.
A hunter ring (iLevel 365), dps caster necklace (iLevel 365), Plate Tank Feet (365), and melee dps necklace (365) with 136 expertise and 201 strength. All four items are sold for gold.
The best value of these vendors is definitely for those who are going after the Mountain of Mounts achievement. They sell writ of commendations for all major city factions increasing reputation by 250. Farming these allow players to reach exalted with a city to buy the mounts. Most players level 85 are revered with all cities via quests anyway. These writs of commendation are sold for 30 Marks of the World Tree each. Players can basically get one commendation daily.