As far as I'm aware, recent browsers don't permit sites to access the history. I know of the history.previous / history.next, but these are only permissible when using local content such as plugins, or local webapps. But now that I think of it, couldn't a website load a bunch of web URLs in a hidden frame, and then analyze said URLs's CSS properties to see if they have been visited before? If that's possible, that would be a semi-transparent way to observe where the user hangs out on the internet, I suppose.