Yeah, I'm now getting the full-screen advert, too. It's really, really annoying, because it asks me "Do you want to navigate away from this page?", I click "No," and then it does anyway! And proceeds to say "Are you sure? I have a surprise for you!" which is not only annoying but also really, really creepy.
Is something wrong with RAF? Are we getting viruses or something?
BTW, I tried fully closing down the browser and opening it again. No luck. And I know it isn't my computer, because I've gotten this problem on two separate computers.