jQueryの-moz-transformから回転角度を抽出する方法は?

$('.element').css("-moz-transform")

function getRotationDegrees(obj) {
    var matrix = obj.css("-webkit-transform") ||
    obj.css("-moz-transform")    ||
    obj.css("-ms-transform")     ||
    obj.css("-o-transform")      ||
    obj.css("transform");
    if(matrix !== 'none') {
        var values = matrix.split('(')[1].split(')')[0].split(',');
        var a = values[0];
        var b = values[1];
        var angle = Math.round(Math.atan2(b, a) * (180/Math.PI));
    } else { var angle = 0; }
    return (angle < 0) ? angle + 360 : angle;
}

angle1 = getRotationDegrees($('#myDiv'));
angle2 = getRotationDegrees($('.mySpan a:last-child'));