Put popped popcorn, marshmallows, gumdrops, and pecans (optional) in large bowl. Melt butter, add sugar and Karo, bring to a boil, stirring and simmering 3 minutes, add vanilla, pour over popcorn. Mix well, let stand 2 minutes to cool. Press into buttered ring-mold. Unmold onto wax paper. Decorate with cut gumdrops. Or make balls with slightly dampened hands.