Dammit, just happened again. It's a Discover Card ad on the All Comments page, that takes over and won't go away, even with refreshing. It only disappears with a hard refresh.

It is ads like this which is why I use the Ad Block to begin with. I don't mind ads as long as they stay in the assigned box but these take over the entire page.

I just reported it to AdBlock. We'll see what they respond.