Danbury firefighters knocked down a fire late Saturday at the former Stop and Shop building on Newtown Road, now slated to become a ShopRite. Crews arrived around 10:30 p.m. and found a fire in a large refrigeration unit that had spread to the roof. Mutual aid was called in due to the building’s size. Sprinklers helped slow the fire. One firefighter suffered a minor cut. The cause remains under investigation.