After blocking similar bills over two years, the House of Representatives voted 75 to 66 for final passage Thursday of a measure variously derided as a windfall for a major energy company and praised as a responsible first step toward stabilizing the finances of Connecticut’s last nuclear plant. The bill would permit, not require, state energy officials to change the rules for how Dominion Energy sells electricity from its nuclear plant, Millstone, whose profits have eroded as energy prices have been depressed by competition from electricity generated by relatively cheap and plentiful natural gas.