Facebook pages with URLs that take the form of facebook.com/<name> (e.g. https://www.facebook.com/muse) can have URLs linking to specific "tabs" e.g. https://www.facebook.com/muse/photos_stream or https://www.facebook.com/muse/info.
These are not currently cleaned up and are left as is.
Review cleanup of Facebook URLs
Strip "/about" from Facebook URLs