Window Shopper for Firefox allows you to instantly compare prices on any product on 3,200 U.S. online stores, including Amazon and eBay. If it finds a deal, it will show it. Otherwise, it will show you similar products you may also be interested in. After you install Window Shopper, you will see a "See Similar" icon appear next to product images. Just click on the icon and the Window Shopper window will appear, presenting deals and visually similar products from hundreds of online stores.