This is a very good extension, I have been using it for a while. It is very much the best of both worlds, using cookies to login, then deleting them when you leave the site. You don't have to worry about whitelists, etc.
But without whitelisting, I wouldn't know how much of the web is completely broken without cookies, where by "broken" I mean a blank page, or just a little strip of the template. This includes blogs, one-off demos, and other sites that don't require (or even offer) log in or settings of any kind.
I can only conclude that some common frameworks depend on cookies for their own operation, and that in many cases the developers aren't even aware of the "problem".
