Spray a large roaster pan with non-stick vegetable spray. Place popcorn in pan and set aside. Combine brown sugar, corn syrup, butter and molasses in a medium saucepan; bring to a boil over medium heat. Cook for 5 minutes, stirring once. Remove from heat; stir in vanilla, baking soda and salt. Pour hot mixture over popcorn, stirring to coat. Bake at 250 degrees for one hour, stirring every 15 minutes. Remove from oven; stir to break up. Cool for 15 minutes. Store in an airtight container for up to one week.