I think it's something I heard him say out loud in one of his earlier lectures at Yahoo. More recently, he's stated that "he used to think the browser was the most hostile programming environment ever devised, but then he found out about mobile programming" - http://www.javaworld.com/javaworld/jw-09-2007/jw-09-rwekeyno...
I've heard Crockford use that quote in a few Yahoo! talks (when I used to work there). It's probably on one of his slides from either: "Javascript: The Good Bits" or one around the same time.