Speed Up Fire Leaf Farming

The first step is to learn Northrend Herbalism, you can learn it from Edward Egan at the old Dalaran. (43.16, 33.72)

Fire Leaf farming can only be farmed here. A flower there is near water. 

Northrend Herbalism Dalaran

To speed up the farming you can use:
Darkmoon Firewater: Allows faster gathering of resources and slightly increases your size for 1 hour (5 min. cooldown)

Fire Leaf  Route 1 – Borean Tundra

There is only this route to farm Fire Leaf. you also find Goldclover flowers in the area. Follow the water around and farm a lot of them. The Fire leaf is also called Firethorn on the map. 

Fire leaf Farming Borean Tundra