Prior to the 1990s, authorities routinely looked the other way as Bay Area families piled into their station wagons and headed to San Francisco’s Chinatown District to score illegal fireworks each July 4th holiday — everything from sparklers and poppers to bottle rockets and M-80s. — Dating as far back as the late 1960s, Chinese street gangs have controlled San Francisco’s illegal firework trade, centered around Chinatown. The illegal market hit its peak in the mid-‘80s when illegal firecrackers and explosives could be scored from vendors up and down Grant Avenue or from teenage gang members…