Shooting fireworks was John Adams' idea
Shortly after the Declaration was signed, Adams wrote to his wife, Abigail, that the date:
“... will be the most memorable epoch in the history of America. I am apt to believe that it will be celebrated by succeeding generations as the great anniversary festival. It ought to be commemorated as the day of deliverance, by solemn acts of devotion to God Almighty. It ought to be solemnized with pomp and parade, with shows, games, sports, guns, bells, bonfires, and illuminations, from one end of this continent to the other, from this time forward forever more.”
Source: "Letter from John Adams to Abigail Adams, July 3, 1776, Adams Family Papers, Massachusetts Historical Society at the American University of Washington, D.C.