however "http://static.new.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php" is an invalid URL
Look at the first script here, its a java script. Just try to update it, its not like you've got anything to lose. It probably loads the button using java.
And yes I just tried, it works for me.
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Java is already the recommended install they detected on their site. Maybe you have a cached script or something I don't know but its not working for me, and regardless they should fix that error I pointed out.