bookmark compatible

Looking for a “bookmark us” wich is compatible with IE and firefox ..the javascript code that i have inserted work good only with IE:

<script type=”text/javascript”>
//<![CDATA[

function bookmark_us(url, title){

if (window.sidebar) // firefox
window.sidebar.addPanel(title, url, “”);
else if(window.opera && window.print){ // opera
var elem = document.createElement(‘a’);
elem.setAttribute(‘href’,url);
elem.setAttribute(‘title’,title);
elem.setAttribute(‘rel’,’sidebar’);
elem.click();
}
else if(document.all)// ie
window.external.AddFavorite(url, title);
}
//]]>
</script>

Some good advices or sources?