Armed with a new state law that opponents denounce as a gift to the gun lobby, pro-gun groups are rapidly scaling up their attack on municipal firearms ordinances throughout Pennsylvania, with the National Rifle Association filing suit over gun-control measures in three cities. Philadelphia, Pittsburgh and Lancaster have “openly defied” a 40-year-old state law that forbids municipalities from regulating firearms, said Chris Cox, executive director of the NRA’s Institute for Legislative Action. The …