It's by 65 Media, and unlike this one, it's not directly made by Jim Carrey unfortunately. I happen to like Jeff Bridges' site for that reason: He's making all the content for it himself. (I have no idea if someone helps him put it up on the web, but that's besides the point)
Nonetheless,if you like Jim Carrey's site, check out some others they made in the same sort of wacky, highly-interactive style:
http://www.imaginetheimpossibilities.com/ (for the Fringe TV show)