var agent = navigator.userAgent.toLowerCase();

    var is_opera = (agent.indexOf("opera") != -1);
    var is_opera2 = (agent.indexOf("opera 2") != -1 || agent.indexOf("opera/2") != -1);
    var is_opera3 = (agent.indexOf("opera 3") != -1 || agent.indexOf("opera/3") != -1);
    var is_opera4 = (agent.indexOf("opera 4") != -1 || agent.indexOf("opera/4") != -1);
    var is_opera5 = (agent.indexOf("opera 5") != -1 || agent.indexOf("opera/5") != -1);

    var is_opera6up = (is_opera && !is_opera2 && !is_opera3 && !is_opera4 && !is_opera5);

    var is_mozilla = (agent.indexOf("gecko") != -1);