IE viser billeder, men FF ikke

Jeg er ved at brygge en lille kalender sammen, og i den forbindelse, vil jeg have noget gfx, til at man kan "spole" frem og tilbage i år og måned.

Mit problem er så, at IE viser billederne fint, men ikke FF. Eksempel:

http://martin8.wi8.ots.dk/calendar/dato_test.php (tryk på test hehe).

JavaScript koden er som følger:
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function openCalWindow(selectYearRange)
{
    calWindow = window.open('', '', 'width=630, height=400, status=0');
   
    var rootDoc = calWindow.document.documentElement;
    var headElm = rootDoc.getElementsByTagName(rootDoc.childNodes[0].tagName)[0];
    var bodyElm = rootDoc.getElementsByTagName(rootDoc.childNodes[1].tagName)[0];
   
    if (bodyElm.firstChild)    {
        bodyElm.removeChild(bodyElm.firstChild); }
       
    var scrElm = calWindow.document.createElement('script');
    scrElm.setAttribute('type', 'text/javascript');
    scrElm.setAttribute('src', 'scripts/kalender.js');
    headElm.appendChild(scrElm);
   
    var calContain = calWindow.document.createElement('div');
    calContain.setAttribute('id', 'calendar');
    bodyElm.appendChild(calContain);

    buildCalendarTop(calWindow, selectYearRange);
    buildCalendarMatrix(calWindow, 1);
    calWindow.focus();
}

function buildCalendarTop(calWindow, selectYearRange)
{
    var mainElm = calWindow.document.getElementById('calendar');
   
    var selectYearStart = selectYearRange.split('-')[0];
    var selectYearEnd = selectYearRange.split('-')[1];
   
    var monthBack = calWindow.document.createElement('img');
    monthBack.setAttribute('src', 'scripts/gfx/monthBackUp.gif');
    monthBack.setAttribute('onmousedown', 'this.src = "scripts/gfx/monthBackDown.gif"');
    monthBack.setAttribute('onmouseup', 'this.src = "scripts/gfx/monthBackUp.gif"');
    monthBack.setAttribute('onclick', ''); // HUSK HUSK HUSK

    var yearBack = calWindow.document.createElement('img');
    yearBack.setAttribute('src', 'scripts/gfx/yearBackUp.gif');
    yearBack.setAttribute('onmousedown', 'this.src = "scripts/gfx/yearBackDown.gif"');
    yearBack.setAttribute('onmouseup', 'this.src = "scripts/gfx/yearBackUp.gif"');
    yearBack.setAttribute('onclick', ''); // HUSK HUSK HUSK
   
    var selectYear = calWindow.document.createElement('select');
    selectYear.setAttribute('id', 'selectYear');
    selectYear.setAttribute('onchange', ''); // HUSK HUSK HUSK

    var selectMonth = calWindow.document.createElement('select');
    selectMonth.setAttribute('id', 'selectMonth');
    selectMonth.setAttribute('onchange', ''); // HUSK HUSK HUSK
   
    for(i=selectYearStart; i<=selectYearEnd; i++)
    {
        var opt = calWindow.document.createElement('option');
        opt.text = i;
        opt.value = i;
       
        try {
            selectYear.add(opt, null)
        } catch (e) {
            selectYear.add(opt)
        }
    }

    for(i=0; i<=11; i++)
    {
        var opt = calWindow.document.createElement('option');
        opt.text = setMonthName(i);
        opt.value = i;

        try {
            selectMonth.add(opt, null)
        } catch (e) {
            selectMonth.add(opt)
        }
    }

    var yearForward = calWindow.document.createElement('img');
    yearForward.setAttribute('src', 'scripts/gfx/yearForwardUp.gif');
    //yearForward.setAttribute('alt', '1 år frem');
    yearForward.setAttribute('onmousedown', 'this.src = "scripts/gfx/yearForwardDown.gif"');
    yearForward.setAttribute('onmouseup', 'this.src = "scripts/gfx/yearForwardUp.gif"');
    yearForward.setAttribute('onclick', ''); // HUSK HUSK HUSK

    var monthForward = calWindow.document.createElement('img');
    monthForward.setAttribute('src', 'scripts/gfx/monthForwardUp.gif');
    monthForward.setAttribute('onmousedown', 'this.src = "scripts/gfx/monthForwardDown.gif"');
    monthForward.setAttribute('onmouseup', 'this.src = "scripts/gfx/monthForwardUp.gif"');
    monthForward.setAttribute('onclick', ''); // HUSK HUSK HUSK

    mainElm.appendChild(monthBack);
    mainElm.appendChild(yearBack);
    mainElm.appendChild(selectYear);
    mainElm.appendChild(selectMonth);
    mainElm.appendChild(yearForward);
    mainElm.appendChild(monthForward);
}
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openCalWindow() er så den funktion der eksekveres, når man trykker på Test på siden.

Jeg kan simpelthen ikke se, hvad problemet skulle være:)