We switched our static content (images, thumbnails, CSS, JavaScript, etc) over to a new domain—4cdn.org.
It has a few benefits, but mainly 1) cookieless domains for static content reduces request size, 2) page weight is reduced, 3) security. tl;dr: The site should load a little faster.
This should be 100% transparent to most users since we've updated everything on our end for the change. If you run various browser rice scripts, you're on your own to make them work.