Several people are having the problem. I am not able to post to Facebook. And after I removed the Facebook option and tried to re-connect it, I no longer have any option to do so. I only removed it because it had been inoperative for quite some time, and inconsistent at best.
update: went to another machine and the same behavior there. When I click "Connect with Facebook" on the settings page for Social, absolutely nothing happens, unless you count the page blipping as if it just reloaded very quickly, but no login prompt for Facebook or anything. Something is broken, guys. You need to do something beyond just saying "we cant duplicate it". It's widespread. And nothing is different now that I'm on WordPress 4.0, except that lately, it NEVER posts to Facebook, which is differetn from the usual 10% success rate for Facebook. Meanwhile, Twitter works every time. Seems like Facebook has made some changes that this plugin hasnt kept up with.