Turn off cookies for the Mac. Preview won't work. Your membership stuff might be a bit odd. Logging in won't really do much, but you can still post. I tried to fix this with sessions the other day, but with the page cache the way it is, I had to stop and undo all my work. If found a big sticking point. Cookies will be around for a little while longer. I do plan on getting rid of the requirement if I can.