Show a modal only once.

gistfile1.js

$(function() {
    if( document.cookie.indexOf( "facebookModalPromoShowOnce" ) < 0 ) {
        $( "#dialog-facebook-message" ).dialog({
            modal: true,
            resizable: false,
            show: 'slide',
            buttons: {
                Ok: function() {
                    $( this ).dialog( "close" );
                    document.cookie = "facebookModalPromoShowOnce=true; expires=Fri, 31 Dec 9999 23:59:59 GMT; path=/";
                }
            }
        });
    }
});