I have forgotten all about these ornaments! I made them about 10 years ago and forgot how much fun they were to make.
Very simple! All you need is microwave popcorn (natural; no butter), brown lunch bag, and a glass ornament. Open the popcorn and wipe any excess oil off of about 1 tsp. of the kernels. Take the top off the ornament and add the popcorn. Place ball in paper bag, put in microwave and fold down the top. Start out at 1 minute to see if any kernels has popped. You may need to increase the time. Mine took 2 minutes and I have a smaller microwave. Be really careful when removing from the microwave because of the steam. Replace top of ornament and tie a ribbon around the neck.
As a note: The ornament is not as yellowed as the picture makes it out to be!