Best "focused browsing" addon by a mile, the possibility of getting periodically reminded you may have been sucked into the vortex of a distracting website is killer. This addon should be integrated in firefox so as to fullfill its vision of a a free browser which puts the user first and defends it from destructive corporate interests. @DK you should really try to get in touch with the firefox team, opensourcing this addon (as well as extending your feed-blocking addon) and in general working on a "firewall" against intrusions and distractions on the web should be a top priority of the free software movement.