[richdougherty]

Right, so this site uses CSS selectors to show the user a different colour for each site they've visited.

In the past the site would also be able to access the different style information rendered by the browser and use it to find out which sites you'd visited. Luckily that privacy leak was patched up a while ago: https://blog.mozilla.org/security/2010/03/31/plugging-the-cs...

Now you'd have to do something like use timing attacks on the browser's cache... :)

[btown]

Or, since you're encouraged to hover or click on each highlighted block, Javascript could leak your information once you interact. There's no protection from the human-in-the-loop leaking their own privacy.