https://www.theverge.com/2018/11/12/18087772/firefox-price-wise-test-pilot-mozilla

Firefox is letting users test a new extension that will track prices for certain items and generate browser notifications when the price drops (via VentureBeat). The Price Wise extension is available from Mozilla’s Test Pilot program, and it currently supports five retailers — Amazon, Best Buy, Home Depot, eBay, and Walmart — although more are planned for the future.

Price-tracking services are nothing new. CamelCamelCamel, a service that tracks prices across Amazon is probably the most famous, and Keepa is a Chrome extension that shows price-tracking information on each Amazon page that you visit. These services have the benefit of showing you historical pricing for an item (allowing you to see how special that deal really is), rather than just alerting you to price changes after you begin tracking it. So Mozilla’s Price Wise has a bit of catching up to do in terms of its functionality.