While browsing Ajaxian, I found this article — “Let’s face it, cross site AJAX is a real pain. If you’re going to provide your components as a service, sort of like Google maps, you’re task is not impossible yet still challenging. If you want to mash up your app with other services at the browser level, you’ve got to proxy those services. Put any way, it’s a pain. How to simplify creating truly powerful, cross-site AJAX apps?
Firefox Extensions and AJAX – A Model for Web 2.0?