populateform();

function populateform(){
	document.getElementsByName("your-subject")[0].value = getURLParam("ms");
	document.getElementsByName("your-message")[0].value = getURLParam("mm");
}

function getURLParam(strParamName){
	var strReturn = "";
	var strHref = window.location.href;
	if ( strHref.indexOf("?") > -1 ){
		var strQueryString = strHref.substr(strHref.indexOf("?")).toLowerCase();
		var aQueryString = strQueryString.split("&");
		for ( var iParam = 0; iParam < aQueryString.length; iParam++ ){
			if (aQueryString[iParam].indexOf(strParamName + "=") > -1 ){
			var aParam = aQueryString[iParam].split("=");
			strReturn = aParam[1];
			break;
			}
		}
	}
	return strReturn.replace(/%20/g, " ");
}