How do I move the Facebook Comments plugin down?

David,
The ordering of the plugins should affect the order of display. When you move the JFBCContent plugin down (higher number), it should show up after any plugins before it. The JFBCContent plugin uses the 'onContentBeforeDisplay' trigger, which is the last trigger to fire before actually displaying the article, which means that if it's last, it should be the last thing to modify the article before display (hence, the very bottom).

If you're not seeing any change, make sure you clear any caches after you make the change. You may want to simply disable any caching as well, for the time being, to eliminate that as a possible cause.

Hope that helps,
Alex