But anyway, I spent a few minutes trying to break it on the live site, and was surprised at how graceful things worked, even with knowing what's behind it. I see that it "breaks" when you click from search, to an art piece, then to a related link...and then attempt to go back to search...but after some thought, I think that's totally reasonable. When a user goes down the rabbit hole of 2+ links, how likely is it they're going to care where they were on an infinite scroll, or any other pagination system? And of course, it's probably a minefield of browser errors if the behavior was to keep persisting the iframes and original search window.
On a related note, has Artsy done a lot of data collection in terms of how their signed-in users navigate the scroll? I figure after awhile, if I were a frequent visitor, I would quickly scroll the search and then "favorite" the things I wanted to check out, rather than visiting pieces one by one, and hoping that the "back" button would maintain my place.
(Of course, power users may opt to pop open new windows for each art piece...but that's untenable on a mobile device. Also, Etsy tried that and it in A/B testing, it apparently failed spectacularly)