New hotfix for the Midsummer Fire Festival

Blizzard will apply a new update in the public realms which will restart the missions associated with the Midsummer Fire Festival. This is the way to solve the problem with the achievement: Extinguishing Kalimdor

From Bornakk
We are in the process of applying an in-game fix that will restart all of the quests associated with the Midsummer Fire Festival event and allow players to complete them once again. If you are in the process of completing an achievement such as Extinguishing Kalimdor, this fix will reset your progress and you will need start over. This fix will require realms to be restarted.