Yeah, the link I first placed was to Intel only (the Webkit Nightly builds). I fixed it. It goes to the correct site now. Those builds are actually done by a person who works on TenFourFox.
Interesting... shame they couldn't turn it into 5.1 for pop-up extensions. I see it was uploaded 2 days ago. How old is this?
I'd assume it's pointless reading the webkit blog since it's aimed at Intel Safari.