Or drop it off at a UPS Store or Mail Boxes Etc. They box it up and ship it back to Verizon for free also. If you return it to the FiOS store, they charge $9.99 now - which is utterly ridiculous.
When you return an STB to the store they have to turn around and ship it back to the repair center, even if it is not broken. . . .always throughly test and repair boxes before sending them to another customer. That is why the store charges $10 dollars, to basically box it up and take it down to UPS for you.