The Firestone could be made by any number of bicycle manufacturers through out the years, hard to tell who made your stem. Do you want a modern replacement to get her going, or a correct oem stem for a restoration? Best thing starting I guess, would be buy a digital caliper. Once you accurately the od of the stem and id of the steer tube you will know what will work and what will not. Modern-day replacements should be no problem acquiring, your going to have to search for proper period correct one. You'll use the calipers more then you know later on down the road.
