They are flattened insects that are thicker near the head and skinny near the bottom. They do not have wings and are covered in scales. Their antennae are long and slender. Both have long slender appendages at their bottom, why they are called bristletails.
Silverfish has silver scales covering them, and are found of area with moisture.
Firebrats have a more diverse color of scale, and like very warm places like near heating units.
They both feed onprotein rich and starchy materials. Books, linens, natural fabrics, are considered food for both. They can also leave a damaging yellow stain. They like new homes because building materials are attractive to them.
Sprays and dusts in common hiding areas is the best treatment. They like hiding in wall voids and attics.