Spray 13x9-inch pan and large bowl with cooking spray. If using microwave popcorn, pop as directed on bag. In bowl, mix popcorn and dried blueberries; set aside.
In medium microwavable bowl, place marshmallows, vanilla chips and butter. Microwave on High 1 minute. Stir mixture; microwave on High 1 to 3 minutes longer, stirring occasionally, until all marshmallows and chips can be stirred smooth.
Pour marshmallow mixture over popcorn mixture; stir until evenly coated (mixture will be sticky). Pour mixture into pan. Spray hands or large rubber spatula with cooking spray. Press popcorn mixture in pan. Place in freezer until set, no longer than 10 minutes.
With serrated knife, cut into bars. Store in tightly covered container or wrap each bar securely in foil or plastic wrap.