Over the last two decades, the Web has significantly transformed our lives. Along with the increased activities on the Web come the attacks. A recent report shows that 83% of web sites have had at least one serious vulnerability. As the Web becomes more and more sophisticated, the number of vulnerable sites is unlikely to decrease. A fundamental cause of these vulnerabilities is the inadequacy of the browser's access control model in dealing with the features in today's Web. We need better access control models for browsers. Today's web pages behave more and more like a system, with dynamic elements interacting with one another within each web page. A well-designed access control model is needed to mediate these interactions to ensure security. The capability-based access control model has many properties that are desirable for the Web. This paper designs a capability-based access control model for web browsers. We demonstrate how such a model can be beneficial to the Web, and how common vulnerabilities can be easily prevented using this model. We have implemented this model in the Google Chrome browser.