Java, Mac et parfois plus …

function bookmark(bookmarkurl, bookmarktitle) {
    try {
        if (typeof window.sidebar == "object" && typeof window.sidebar.addPanel == "function") {
            window.sidebar.addPanel(bookmarktitle, bookmarkurl, "");
        } else if (typeof window.external == "object") {
            if (typeof window.external.AddToFavoritesBar == "function") {
                window.external.AddToFavoritesBar(bookmarkurl,bookmarktitle);
            } else {
                window.external.AddFavorite(bookmarkurl,bookmarktitle);
            }
        } else {
            alert('Ooops, I do not know how to create a bookmark on your browser!\nYou have to do it your self!');
        }
    } catch(e) {
        alert('Ooops, I did not manage to create the bookmark on your browser!\nYou have to do it your self!');
    }
}

JavaScript bookmark, Firefox, IE, JavaScript