Are fireworks a hazard to aircraft?
In canada and I assume in a similar way in the United States, fireworks are treated like any other obstacle such as a communication tower, building, or crane. The location and elevation of the firework activity is assessed for impacts to any instrument procedures, airways, minimum altitude areas, etc. and NOTAM to temporarily amend affected procedures will be issued prior to the activity to advertise the changes and their effective periods.

Having said that, this doesn't address the VFR side of things. Operating near fireworks is essentially the same see and be seen idea. NOTAM get issued here all the time for the fireworks activity themselves and they would include a radius from the centre point. Simply avoiding the area is usually sufficient.