I am getting this JS error in my browser console:
TypeError: e.attr(...) is undefined
on the StackOverflow homepage, in this file, line 82:
This has the effect that the two pop-up menus at the top of the page no longer work. Meta SO seems to be unaffected.
Firefox 19.0.2, OS X 10.6.8 (though Safari seems affected too, so I suspect a JS bug).