In a medium saucepan, combine sugar, water, syrup, vinegar, and salt. Cook over high heat until mixture reaches 255 degrees F (hard-ball stage) on a candy thermometer. Stir in vanilla.
Pour over popped corn, tossing gently to coat. When mixture is cool enough to handle, press popcorn into 3-inch balls with lightly greased hands. Cool completely on waxed paper.
