Allow setting GM_XmlhttpRequest HTTP Referer
Allow setting GM_XmlhttpRequest HTTP Referer

Firefox can prevent us from setting the Referer header. Work around
this by setting the header in an observer for the http request.

HasClass0/greasemonkey,Ventero/greasemonkey,Ventero/greasemonkey,HasClass0/greasemonkey,Martii/greasemonkey,the8472/greasemonkey,the8472/greasemonkey,Martii/greasemonkey