When visits Facebook, he's been having issues where the page scrolls on its own. Leo says if it happened everywhere, it could be a stuck down key, but since it only happens on Facebook, that's an indicator for software. Could someone be taking over his account? Leo says probably not. Just in case, however, he should go into his Facebook settings and turn on 2nd factor authentication. Then if someone tries to hack his account, it'll send him a notification asking if he's logging in. If it's not him, they can't log in. Also, when he uses a public computer, he'll need to wipe out the memory cache before he leaves.
This leads to a corrupted memory cache. The files loaded in cache from Facebook could have gotten corrupted. Resetting his browser will fix that.