Pop popcorn, and place in a lightly greased 15-x 10-x 1-inch jellyroll pan. Set aside.
Combine sugar, butter, syrup, molasses, and salt in a large saucepan. Bring to a boil; boil 5 minutes, stirring constantly. Remove from heat; stir in soda and peanuts.
Pour hot syrup over popcorn in prepared pan, stirring until evenly coated. Bake at 200° for 1 hour, stirring every 15 minutes to separate pieces. Cool and store in an airtight container.