A method of modifying an Internet browser interface to provide shopping assistant functionality facilitating on-line shopping at a supported merchant Internet site. A wallet created in accordance with the present invention comprises a database having various user data stored therein under certain predetermined field names. A supported merchant data file identifies a plurality of supported merchants and enables the modified browser interface to determine when a shopper has navigated to a supported merchant web site. For each supported merchant, a rules and mapping file is created that may be used in connection with the wallet to map user-provided information in the wallet to corresponding fields in the merchant's check-out web page. When a user navigates to a supported merchant web site and desires to purchase merchandise and/or services from that merchant, the wallet automatically fills out the merchant's check-out web page(s), thereby simplifying on-line shopping and particularly, the check-out process.