The document discusses the power of browser customization through add-ons. It notes that add-ons can extend browser functionality and provide continuous access to websites even when users are not directly on the site. Well-designed add-ons can help increase user retention on sites. The document provides examples of popular add-ons for services like Delicious and StumbleUpon, and discusses upcoming developments like the Add-ons Marketplace and changes in Firefox 4 that aim to improve the add-on experience.