If by "clean" you mean its fallback behavior without JS is to show a white page with nothing, then it is squeaky clean. :D
Here's plain text for anyone interested: http://urbit.org/posts/overview.md
Edit: it should be easy for us to stick that link inside a noscript tag be default. Issue here: https://github.com/urbit/arvo/issues/149
You're doing a lot of work yourself: loading pages (why not let the browser do that, catch errors, display progress, etc.? Now it shows a spinner and if I hadn't backgrounded the tab already I'd have given up on loading because "clearly the spinner isn't doing anything"); opening links (I can't ctrl+click because, hey, you're handling the opening of links yourself; why not let the browser do that?); changing the title happens only after the new page loaded, which takes 20 seconds, during which time a white page is displayed with the old browser and the new URL already (the browser would change it to "loading new page" for you); and there are some cross-origin resources (alright, the browser doesn't do this, but it's almost difficult to mess that up with the widespread TLS support these days). I probably caught most of my personal things, but the general idea is to be more lazy ;)
The links not opening on ctrl+click is ridiculous (issue here: https://github.com/urbit/tree/issues/10) as are the cross-origin resources. Loading in the title is a good idea (issue here: https://github.com/urbit/tree/issues/11).
Being lazy is good. I'm with you there!
> "Each urbit is a node on _an_ global, encrypted P2P network."