Perfect timing, I'm having an issue on this one as well. No, facebook does not have any special script to allow iframe back/forward. It's built-in browser functionality. For me, my problem lies in multiple iframe's history. Apparently..at least for Firefox..it has no problem handling just 1 iframe for back/forward.... but when it comes to "multiple" iframe..then it acts very weird!
from above code, it makes you "think" you're using "iframe's" history but it's really not...
See my post for more details...