Facebook has had this for ages. And what makes you think that XenForo had this kind of thing first. Nothing XenForo has done hasn't been done before in some way. Well some backend stuff seems unique, but for the end user it is taking a LOT of stuff from facebook, not the other way around. You greatly underestimate facebook.
Well, in all fairness, I think tweakers.net lightbox is 90% of xenforo's, and they had it for years. So ..
It's just how you look at it. I am sure lightbox technology has been around for a while, and the common-sense implementation of it makes xenforo look like tweakers.net, and facebook's like xenforo, and they all look like the one I made in 2006 for my mac pro gallery, which I based on something yahoo demod a year earlier. etc.
As long as facebook doesn't 100% copy, including source code, ..