After you've completed both the Shadow Wardens and Druids of the Talon 150 Mark of the World Tree quest grinds, three new quests will open to you that each require 125 Mark of the World Tree to complete. (Also, please note that if you've reached this point, you may be wondering whether you can complete both the Shadow Wardens and Druids of the Talon daily quests (Into the Fire line and Forlorn Spire line.) You can only complete one line daily, so pick the one that goes quickest for you.)
At the end of each of these three new quests is access to one of the three Molten Front / Firelands vendors that have the new gear and recipes on them. It also opens up access to a couple more daily Mark of the World Tree quests. It looks like the best order to complete them based on number of Marks of the World Tree accumulated is as follows:
1) Call the Ancients
2) Additional Armaments
3) Filling the Moonwell
This order is simply a function of Call of the Ancients netting 3 Marks daily, Additional Armaments 2 marks daily, and Filling the Moonwell 0 Marks daily.
How to get to Firelands Entrance
Firelands Dailies Guide
Review of Firelands Dailies Plus Some Inspiration
Shadow Wardens vs. Druids of the Talon - Which one Do I Choose?