Cook the bacon in a large nonstick skillet over medium heat until crisp. Drain on paper towels, then crumble finely. Pour the fat from the skillet into a spouted measuring cup. Add vegetable oil as needed to make 1/4 cup fat; if there is more than 1/4 cup bacon fat, pour off the extra. Set the skillet aside.
Pour the bacon fat into a stockpot (12-quart or larger) over medium heat. Add a few popcorn kernels; when they begin to sizzle, add the remaining kernels and shake to coat in the oil. Cover the pot and cook, shaking frequently, until the popping has almost stopped (a pop every second or two), about 5 minutes. Remove the pot from the heat and keep covered.
In the skillet used for the bacon, melt the butter and maple syrup over medium-low heat, stirring to loosen any browned bits on the bottom of the skillet. Stir in the crumbled bacon and then pour the mixture over the popcorn; toss well to coat all of the kernels. Season with salt and toss again. Serve immediately.