Keepa for Chrome, Firefox, Edge, and Opera provides price history charts for millions of Amazon products and can alert you when a price drops.
Keepa will watch any Amazon product for you and alert you by email, web push, telegram, or RSS when the price drops. You will need to log in with a user name and password to take advantage of this feature.
You can set up the desired price, new or used, show the item on Amazon, and delete tracking at any time.
Keepa also keeps a list of great deals online, so if you don't need alerts, you could shop for deals anytime.
Opera users will need to install Install Chrome Extensions, then download from the Google Chrome link.
Avira Safe Shopping for Chrome, Edge, and Opera is an extension to ensure your safety and privacy while shopping and looks for better deals from other websites.
Klarna (Formerly Piggy) for Chrome and Android finds the best coupons and promotional codes and applies them automatically while you shop, saving you money.
Fakespot for Chrome, Firefox, and Edge analyzes product reviews for reliability, helping to protect you from bad sellers and fake reviews on Amazon, etc.