Annoying message popup on Facebook for iPhone?

This just started happening on my iPhone - when someone sends me a message, a little "bubble" with their FB portrait picture appears on the screen. And it will not go away! Even if I answer the message, or delete it, the bubble is still there! If I leave my finger on it for a few seconds, there's a message saying "Drag down to close", but when I do that nothing happens - the bubble hits the bottom of the screen, it doesn't close. Can anyone help me get rid of this incredibly annoying thing!

Go to settings and turn off "Chat heads"