rem: var button = buttons.firstChild.nextSibling; 
add: var button = buttons.firstChild; 
context:   getLastVisibleBookmark: function ()  {    var buttons = document.getElementById("bookmarks-ptf");    var button = buttons.firstChild.nextSibling;    if (!button)      return null; // empty bookmarks toolbar    do {      if (button.collapsed)        return button.previousSibling;      button = button.nextSibling;    } while (button)    return buttons.lastChild;  },
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/9273880c70ae226f38751ca490af247420ca0d1e/bookmarksMenu.js/buggy/browser/components/bookmarks/content/bookmarksMenu.js