Systems, computer-implemented methods, and computer-readable media for a customizable redemption header for merchant offers, such as online coupons, across browser instances are provided. In some embodiments, a user may open a merchant website in a first browser instance executing on a user device. An offers website may provide offers, such as online coupons, in a second browser instance executing on a user device. When a user selects an offer, an offer identifier may be stored in a browser-accessible storage device. The modification to the browser-accessible storage may be detected and a customizable redemption header having an offer redemption identifier, e.g., a coupon code, and instructions may be provided on the merchant webpage in response to the detection. Additionally, the customizable redemption header may provide user feedback requests upon submission of the coupon code.