Prepare popcorn according to package directions; remove unpopped kernels. Transfer popcorn to a roasting pan.
In small saucepan, combine butter, blue cheese, hot sauce and celery salt. Cook over medium heat until butter and cheese are completely melted, stirring frequently.
Drizzle butter mixture over popcorn; stir to coat well. Bake in a preheated 300°F oven 5 minutes, stirring halfway through. Serve hot.