Slashdot reports, that CSS History Sniffing is back – this time utilizing the latency that your browser shows when you have visited a site already. The time a browser takes to respond differs when the resource that is linked in a page is already in the browser cache. Of course that only works when you actually fetch the resources. As i described earlier, there is a Firefox extension that protects you: Request Policy. This extension lets you choose which sites may refer to which other sites. It’s a bit tedious to get started, but it protects you not only from the ever-watching eye of social networks that load “like” buttons everywhere, but also from this renewed threat.