I’ve done it so many times, and it is very easy AND much healthier. All you need is a plain brown paper bag. You can add oil and/or salt if you like, but it isn’t necessary. If you’re using a lunch-size paper bag, measure about ¼ to ⅓ cup popcorn kernels into it. Fold the top down, place it upright in the microwave, not on its side like you would a bag of microwave popcorn. The first time you make it, set the time for 3–4 minutes, but watch it closely and remove it from the microwave when popping slows down. Note the time, and use that as a guide for future popping.
Besides being better for you, it’s cheaper. It’s also great if you want to use the popcorn to make other things, like popcorn balls or caramel corn, and don’t want the popcorn to be greasy or too salty.
When I’ve popped corn this way, the bag has never scorched, let alone caught on fire. I think it’s perfectly safe if you just keep an eye on it like you would store-bought microwave popcorn.