<script type="text/javascript" language="JavaScript">
    function do_replace(){
        HTML_AJAX.replace("something", "index.php?key=value"); // index.php will have html mixed with JS and paste it to the div "something".
    }
</script>
<div id="something" onclick="javascript:do_replace()">This text is to be replaced</div>

BLA BLA BLA some text maybe a <div> or something
<script type="text/javascript" language="JavaScript">
    alert("this has worked before, but stopped working on FF4&5 still works on Chrome Android etc.");
</script>

var good_browser = false;

var good_browser = (navigator.product == 'Gecko');

if(navigator.product == 'Gecko'){
        var regex_gb = /Firefox[/s](d+.d+)/;
        if(regex_gb.test(navigator.userAgent)){
         var ffversion = new Number(RegExp.$1);
            if(ffversion >= 4){
                var good_browser = false;
            }else{
                var good_browser = true;
            }
        }else{
            var good_browser = true;
        }
    }else{
        var good_browser = false;
    }

HTML_AJAX.js
HTML_AJAX_lite.js
util.js.