Loading External JS File onClick not working in Firefox

I have 4 images that when clicked load an external javascript file onto the page.  Here is the code for it:

                 <script language="javascript">
                  function returnObj(name)
                  {
                        var obj = null;
                        
                        if(document.all)
                        {
                              obj = document.all[name];
                        }
                        else if(document.getElementById)
                        {
                              obj = document.getElementById(name);
                        }
                        else if(document.layers)
                        {
                              obj = document.layers[name];
                        }
                        
                        return obj;
                  }

                  function switchText(name)
                  {
                        var js = returnObj('remoteJS');

                        js.src = 'test'+name+'.js';
                  }
            </script>

            <script language='javascript' id='remoteJS'>
            </script>

            <a onclick="javascript:switchText('one');" style='cursor:pointer'>
                  <img src='img1.jpg'>
            </a>
            <a onclick="javascript:switchText('two');" style='cursor:pointer'>
                  <img src='img1.jpg'>
            </a>
            <a onclick="javascript:switchText('three');" style='cursor:pointer'>
                  <img src='img1.jpg'>
            </a>
            <a onclick="javascript:switchText('four');" style='cursor:pointer'>
                  <img src='img1.jpg'>
            </a>

In the external js files I have some alerts just to test if it works:

                 alert('test 1');


So all of this works correctly in IE, but in Firefox it does nothing.  I am wondering what the difference is.  Is this a security issue (loading from an external file)?  This is probably an easy question, but I rarely use javascript and hardly ever from an external file.  Any help would be appreciated.

- vlad