This isn't a search feature; it's a browser feature. There's no real way for them to implement this in a cross-browser way; they could load a hidden iframe for

This isn't a search feature; it's a browser feature. There's no real way for them to implement this in a cross-browser way; they could load a hidden iframe for the first result, but it looks like they're actually rendering it in the background, not just pre-caching it, so it wouldn't have as much of an effect. Other browsers could probably implement this just as well, eventually.