Since upgrading my main system to Yosemite, Facebook like and share buttons no longer work -- with the share button, the window pops open, but then hangs with no content. If I open Web Inspector, there are no errors displayed. Also, if I browse to Facebook, the login screen loads correctly, but after signing in it also hangs up trying to get to the next page. All of these actions do work correctly in Chrome under Yosemite, and I never had these problems before upgrading to Yosemite.
Never mind! Facebook updated something today and it now works again.