Browsers aren't extensible.
Content-Security-Policy: default-src 'self' ajax.googleapis.com
var origin = window.location.origin;
page.addEventListener('fetch', function(e) {
var url = e.request.url;
if (origin !== url.origin) {
// block the network request
e.preventDefault();
}
// otherwise, allow the network request through
});
Bookmarking a site == installing an 'app'
<3 - @steveklabnik