JavaScript Cross Browser Issue

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Javascript

Hi,
I am making an application,in which i am making combobox(ie dropdownlist) dynamically by javascript
I have a div on my page and appending the generated combobox on that div
The code is working fine as of the required functionality in IE and chrome,but when i checked it on FireFox,it is not making any dropdown,i checked it on console of Firebug it is showing the error that div is not defined can any one help???

var numi = document.getElementById('theValue');
var ni=document.getElementById('mydiv');
        var num = (document.getElementById('theValue').value - 1) + 2;
        divname = ni;
        numi.value = num;
        var newdiv = document.createElement('div');

        var divIdName = 'my' + num + 'Div';
        //Calculating Major and Minor Count
        var majorcount = parseInt(document.getElementById('majorcount').value);
        newdiv.setAttribute('id', divIdName);
        if (ni.id == "addmajordiv") {
            var select = document.createElement('select');      
select.setAttribute("name", document.getElementsByTagName('select')[j].name);
                select.setAttribute("style", "width: 350px;height:35px;");
            var link=document.createElement('a');
            link.setAttribute('onclick', 'removeElement(' + divIdName + ')');
            link.setAttribute('style', 'font-size: 120%;font-weight: bold');
            link.setAttribute('href', '#');
            link.innerText = "Remove";
      

            for (var i = 0; i < document.getElementById('all').length; i++) {
                var option = document.createElement("option");
                option.text = document.getElementById('all')[i].text;
                option.value = document.getElementById('all')[i].value;
                try {
                    select.add(option, null); //Standard
                    select.id = "MajorCourse";
                    select.name = "MajorCourse";
                } catch (error) {
                    select.add(option); // IE only
                }
            }
            newdiv.appendChild(select);
            newdiv.appendChild(link);           
            majorcount = majorcount + 1;
            document.getElementById('majorcount').value = majorcount;
        }