If by fancybox you mean the image overlay that lets you see it in full size and in full screen, then yes. This is what happens when I click on a locally stored(*) image: the background gets darker, as it should, but nothing else is right. Notice how the scroll bar at the right weirds out, for instance.
I'm using the latest version of Firefox. Don't know how other browsers are dealing with it.
(*) "locally stored" in the Space Engine site, I mean, as opposed to stuff hosted in imgur and similar sites.