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That comment is in Primer which is a very small piece of JavaScript loaded at the beginning of every page.

Thanks, did FB ever release anything more from Primer? https://gist.github.com/376039

Or is this it? I didn't see the comment.

The Javelin JS framework used for Facebook Lite.

That it is, it just excludes the comment at the header. It has actually changed a bit since then, but that is still pretty much it.