To insert an "Add to favorites" link, add a Widget block containing the following code (remember to edit the text marked in yellow)
<a href="#" onclick="bookmark()">
Add to favorites</a><script>
function bookmark(){
var url = "https://www.sitew.com";
var title = "SiteW.com";
if (window.sidebar) {window.sidebar.addPanel(title, url, "");} else if( window.external ) { window.external.AddFavorite( url, title);}
return false}
</script>