Speak to a Fireworks Coordinator at 269, 106, 146 near the Kelethin Regional Bank in Kelethin (Greater Faydark) to begin this quest. The coordinator will only offer the quest after you obtain a free Festive Sparkler from the Marketplace.
Light 10 celebration fireworks. These look like bottles that you can interact with by clicking on. They are found outside all over Kelethin.
This city is a bit harder to find the launchers in. Try checking on the platforms outside of buildings, next to merchants, near the elevators and near the ramps and stairs.
After you get all 10 the quest will automatically complete. The quest is repeatable.