Javascript in IE6 vs. Mozilla Firefox

Hi Experts,

I am having some trouble with a scrip working in Mozilla which works fine in MS Internet Explorer.

On a page I have a “main image” and a number of thumbnail images.  A typical thumbnail image has the following html associated with it:

<a
href="jpeg_files/pic_landscape_w&w_03.jpg" class=content-thumb
onClick="return showPic(this,311,454)" onMouseOver="movein(this,'Dove Lake','Tasmania','')" onMouseOut="moveout(this)"><img
src="jpeg_files/pic_landscape_w&w_tmb_03.jpg" width="50" height="50" border="0"></a>

As you can see, there is a onMouseOver and an OnMouseOut which works fine but the onClick is the problem.  When you click the thumbnail it executes the following Javascript:

function showPic (whichpic,iwidth,iheight) {
     if (document.getElementById) {
            document.getElementById('placeholder').src = whichpic.href;
            document.getElementById('placeholder').width = iwidth;
            document.getElementById('placeholder').height = iheight;
            
            alert (reference)
            alert (whichpic.alt)
            alert (whichpic.href)

            boxdescription_1a.innerHTML=document.getElementById('boxdescription_1').innerHTML
            boxdescription_2a.innerHTML=document.getElementById('boxdescription_2').innerHTML
            boxdescription_3a.innerHTML=document.getElementById('boxdescription_3').innerHTML
                        
            if (whichpic.title) {
                  document.getElementById('desc').childNodes[0].nodeValue = whichpic.title;
            } else {
                  document.getElementById('desc').childNodes[0].nodeValue = whichpic.childNodes[0].nodeValue;
            }
            return false;
            } else {
      return true;
            
      }
}

In Internet Explorer, it works fine…. The image placeholder is resized and the images source is changed to the href of the thumbnail.

In Mozilla, it also does the above…. But it then goes a step further and invokes the href and opens the image (in the above case:  jpeg_files/pic_landscape_w&w_03.jpg) into a screen of its own…. as I guess you would expect it would do if all the javascript stuff wasn't there....

Does anyone have any suggestions to this “problem” in Mozilla?