The Connecticut State Library site states:
All fireworks except for sparklers and fountains are illegal in Connecticut. Violators are subject to a fine of up to $100 or up to 90 days in jail or both. Only persons sixteen years of age or older can buy, sell, use or possess sparklers or fountains. See Connecticut General Statutes section CGS 29-357. Anyone conducting or sponsoring a supervised display of fireworks must get a permit from the State Fire Marshal.
These fireworks may have been legal to ignite, but left on the sidewalk, they become litter.