in general , one aspect of the subject matter described in this specification can be embodied in a method that includes loading one or more web pages from a remote server site using a web rendering engine on a local computer , wherein the one or more web pages are confined to a sandbox within the local computer ; retrieving data from outside the sandbox within the local computer ; and adding functionality , with respect to the one or more web pages , to a user interface by translating the data from a first data format employed by the local computer and sending the translated data to the web rendering engine . other embodiments of this aspect include corresponding systems , apparatus , and computer program products .