Login with Facebook does not work at all, just leads to "#"

I've got the right API and secret, but when I click the Facebook tab to try to log in to post comments, the "Login with Facebook" icon shows up, but when I click it it doesn't lead anywhere. The HTML shows a link of href="#".

I've tried activating the alternate facebook login addon to no effect.

Logging in with Wordpress, Twitter, and Google all work just fine.

What gives?