In a large saucepan over medium heat, cook and stir the marshmallows, butter and oil until the marshmallows are melted. Remove from the heat; stir in vanilla and salt.
In a very large bowl, combine the popcorn, M&M's and peanuts. Pour marshmallow mixture over popcorn and mix well. Press into two greased 13-in. x 9-in. pans. Let stand for 2 hours or until set. Cut into bars and remove from pans. Store in an airtight container.