I read this article which is about how to improve the browser for hybrid Web applications i.e secure Ajax mashups.
"Current Web browsers weren't designed to easily and securely get content from multiple sources into one page.Developers have stretched the available tools to fit the task and has put strain on the resulting applications with respect to security and scalability. Also several browser improvements being proposed to remedy the situation."
The detailed explaination of secure Ajax mashups can be read in :Shaping the future of secure Ajax mashups