<script> 

    var editor1=document.getElementById('<%=Editor1.ClientID%>');

    var editdoc = editor1.GetDocument(); 
    var head = editdoc.getElementsByTagName("head")[0];
    var htmlbase = editdoc.getElementsByTagName("base").item(0);
    if(htmlbase) { 
        try{ 
            head.removeChild(htmlbase); 
            htmlbase = null;     
        } 
        catch(er) 
        { 
        } 
    }
    
    if (!htmlbase)
    {
       var newbase = editdoc.createElement("<BASE href=\""+str_BaseHref+"\" target=_blank>");
       head.appendChild(base1);
    }

</script>