I mean there might be festive nights like New Year eve, when there is spectacular display of colorful firecrackers in the sky, but when there are flights descending or ascending near a city with an altitude of 3000 feet, I feel that it is risky enough to fly flights that low.
Typical fireworks simply don't go that high. The world record for the highest firework ever is 3,700 feet. Most fireworks only reach 200-500 feet before exploding. The very biggest commercially available fireworks may be able to reach 1,000 feet.
Firework displays are basically treated like cranes or any other obstacle that might be erected in the vicinity of an airport. A NOTAM will be issued, and pilots will know not to fly near the display. Not to mention that they're pretty easy to see, given how bright the typical firework is. But it rarely matters, since the only time a typical plane will be flying that low is if it's just about to land or had just taken off.