bidding_status.user.js

// ==UserScript==
// @name        Bidding Status
// @namespace   leafnode
// @include     http://allegro.pl/myaccount/bid.php
// @version     1
// @grant       none
// @require     http://ajax.googleapis.com/ajax/libs/jquery/2.1.4/jquery.min.js
// ==/UserScript==

jQuery('#items-list tbody tr').each( function ( i ) {
  var el = ''+jQuery(this).find('td:nth-child(2)').find('.uname a').attr('href');
  var winning = (el.indexOf('show_user.php') != -1);
  if (winning) {
    jQuery(this).append('<td style="background-color: green; border: 1px solid silver">WIN</td>');
    console.log("Winning!");
  } else {
    jQuery(this).append('<td style="background-color: red; border: 1px solid silver">LOSE</td>');
    console.log("Losing!");
  }

});