Speak to a Fireworks Coordinator at -64, 148, -14 near the center of town in New Halas (Frostfang Sea) 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 New Halas.
After you get all 10 the quest will automatically complete. The quest is repeatable.