The mockup isn't supposed necessarily be the way things actually will be. It it simply proves what can be done with HTML. I recommend using Chrome or Firefox, but the appearance and functionality are not the same even between the two. Disclaimer: the code quality is almost as bad as the appearance of the web page. It was a quick job, and it wasn't even really intended for anyone to see at first ;)
You can download it from this sourceforge project page. There are some fun things you can do with the search function, so look in the html file to see what those things are! The sidebar is auto-hidden on the right, so it works best in full-screen.
Anyway, now that we have a way to try out ideas for real, start coming up with those ideas, everyone :)