I'm having the same problem. I have Adblock Plus 1.3.9, but it doesn't stop the popup, just grays out the text in the popup, and the screen is still taken over by the popup. I've heard noscript will block it, but that has other costs. It would be great if ADP would catch it, or better, someone at yahoo/facebook would realize how intrusive this is.
I thought of just agreeing to the facebook ad terms, but I don't want what it offers.
I would simply stop using my.yahoo and go to another newsreader, but my email is through yahoo and I like it on one page. That will have to change soon.
So, at present it is a regular annoyance that serves no constructive purpose. It's ironic that yahoo mail blocks spam, and then yahoo.com spams you right back, in a worse way.