Fireworks were a part of observances from the very first
On July 4, 1777, Philadelphia celebrated the first anniversary with an official dinner for the Continental Congress. Ships in Boston, Baltimore, Savannah, Charleston, Norfolk and New York City harbors were decked with red, white, and blue bunting.
In Bristol, Rhode Island, 13 gunshots were fired, once at morning and again as evening fell. At other events, historians recorded toasts, 13-gun salutes, speeches, prayers, music, parades, troop reviews, and, yes, fireworks.
Source: James R. Heintze, the "Fourth of July Celebrations Database" at the American University of Washington, D.C.