The tailor in Eldfell - City Center needs five firebird feathers to make a garment. Get them for him and you will be rewarded.
On the iPod/iPhone version of this game this quest is called "Find Five King Firebird Feathers."
This is a fairly simple quest. You should find enough firebirds around the River of Lava and Lava Lake areas. You also get one from Auntie Rilla in the Fallen Cemetery if you complete her quest. Failing that, try the Caves of Fire. Every firebird drops one feather when killed. They cast spells from a distance so the Paralyze spell can help you get close enough to kill them. Buff up your magic resistance before closing with them and you will sustain less damage.
Once you have five feathers, return to the tailor and get your reward (a nifty belt).
The Lavabird feather that you get from the Caves of Fire can be sold to the tailor for a large amount of cash.