Except that Javascript cannot access that, unless some glaring design flaws have been made.
If you disagree with me, and believe it can, I would just love to see a webpage that dumps out valuable data inside my browser. I'll visit it without any browser plugins using the same session I have been using for over a month, promise!
http://en.wikipedia.org/wiki/Online_banking
http://en.wikipedia.org/wiki/Cross-site_scripting