User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; WOW64; en-US; rv:2.0b1) Gecko/20100630 Firefox/4.0b1
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.1; WOW64; en-US; rv:2.0b1) Gecko/20100630 Firefox/4.0b1
Firefox 4.0b1 appears to be sending the HTTP security key headers for websockets as "Sec-Websocket-Key1" and "Sec-Websocket-Key2" instead of "Sec-WebSocket-Key1" and "Sec-WebSocket-Key2".
The spec from http://www.whatwg.org/specs/web-socket-protocol/ indicates that the 'S' in "Socket" should be capitalized.
This has been fixed in a later version of Firefox 4 (and is no longer relevant to WebSockets in version 6 and later).