Preheat the oven to 250 degrees F.

Coat a large jelly roll pan with cooking spray.

Combine the butter, corn syrup, sugar and molasses in a medium saucepan; bring to a boil over medium heat. Cook for about 5 minutes, stirring once.

Remove from the heat; stir in the baking soda, vanilla and salt.

Place the popcorn in a large bowl and pour the sugar mixture over it in a steady stream, stirring to coat.

Spread the popcorn mixture into the prepared pan.

Bake at 250 degrees F for about 1 hour, stirring every 15 minutes.

Remove from the oven and stir to break up any large clumps. Let cool for about 15 minutes and serve warm or at room temperature.