Combine sugar, syrup, and water in a medium saucepan over medium heat. Cook 1 minute or until sugar dissolves, stirring constantly. Cook, without stirring, until candy thermometer registers 270° (about 8 minutes). Stir in molasses and butter; cook until thermometer registers 290° (about 5 minutes). Stir in baking soda, vanilla, and salt. Stir popcorn into boiling syrup mixture. Working quickly, pour popcorn mixture onto prepared pan; spread to ¼-inch thickness using a wooden spoon coated with cooking spray. Cool completely; break into large pieces.