There's an extension for Safari as well (submitted for approval, but here's a link in meantime): http://www.mediafire.com/?li7j7965f67ryrg

Also, I wanted to give credit to Matt Blodgett (http://www.mattblodgett.com/2009/07/rotten-tomatoes-netflix-...). He had the closest thing to what I was looking for (in that case it was a greasemonkey script that is a bit outdated). I re-used the portion of his code that translates movie names from Netflix, to the corresponding RT URL.