Preheat oven to 250°F (120°C).

Line two large baking dishes (e.g., 9x13 inch pans) with foil and coat with cooking spray.

Fill each baking dish with 7 1/2 cups of popped popcorn.

In a large, heavy-bottomed saucepan, combine butter, brown sugar, molasses, corn syrup, ground ginger, cinnamon, and salt.

Heat the mixture over medium heat, stirring frequently, until it boils.

Boil the mixture for 5 minutes, stirring frequently.

Remove the saucepan from the heat and add baking soda, stirring to combine.

Pour the butter-sugar mixture evenly over the popcorn in the baking dishes.

Toss the popcorn to coat it thoroughly with the mixture.

Bake in the preheated oven at 250°F (120°C) for 1 hour, carefully stirring the warm mixture about every 15 minutes to ensure even baking and prevent burning.

Remove the baking dishes from the oven and allow the gingerbread popcorn to cool completely before serving.