Try it yourself editor

Code

<html>
    <head>
        <title>Disable Text using JavaScript</title>

function disableSelection(target) {
                if (typeof target.onselectstart != "undefined") //IE route
                    target.onselectstart = function () { return false }
                else if (typeof target.style.MozUserSelect != "undefined") //Firefox route
                {
                    if (typeof target.style.MozUserSelect != "none") {
                        target.style.MozUserSelect = "none";
                    }
                }
                else //All other route (ie: Opera)
                    target.onmousedown = function () { return false }
            }

</script>
        <style type="text/css">
            {
                -moz-user-select: none;
            }
        </style>

</head>
    <body>
        <form id="form1">
            <div id="mydiv">
            Welcome to Gyan Sangrah: A one stop shop for people preparing for technical interviews.
            Gyansangrah is an online resource comprising all the possible questions you may
            face during your technical interview round. Gyansangrah also provides you with live
            examples to make concepts easier to understand.
            </div>

Output