<a href="http://site.com" onclick="window.external.AddFavorite(this.href,this.innerHTML);">Add Favorite and Go-To-There</a>
The first param to AddFavorite is the URL, the second the text to offer up for saving. So this inline JavaScript is reusable in the sense that it will pull those values dynamically from the anchor link itself.
Test that for firefox :
if you use PHP or ASP you can detect browser with
HTTP_USER_AGENT
variable and send the correct code for make the link…