Add the sugar, water, marmalade, salt, light corn syrup and vinegar to a saucepan and stir to combine. Bring to a boil, stirring until sugar dissolves. Let cook until a thermometer reads 250°F, the hard ball stage.
Place the popcorn in a large bowl and slowly pour the sweet mixture over-top while mixing thoroughly.
Using greased hands, shape the popcorn into 2½-inch balls and let set.
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/sweet-marmalade-popcorn-balls