It does nothing, the page is just blank. The address bar and the cursor indicate it's loading, but nothing happens, it just remains blank; sometimes it'll be for a few hours, sometimes it'll be the whole day.
It hasn't happened again yet (though it kind of seems to on a weekly basis), but if and when it does, I'm going to see if AdFender, or any other kind of add-on is somehow playing a key factor in it.