Upon loading the Facebook site, the page shakes, quickly and quite noticeably, left and right once or twice, then settles into place. I haven't seen this happen on any other website.
FWIW, the behavior occurs on http://www.facebook.com but NOT on http://lite.facebook.com ...The lite screen doesn't have two areas for userid/password.
I tried rebooting and clearing the cache. The behavior persists. To repeat: this is NOT a problem, per se. Just a curiosity.