rem: recentTabsItem.setAttribute("disabled", browser.getUndoList().length == 0); 
add: recentTabsItem.setAttribute("disabled", !browser || browser.getUndoList().length == 0); 
context: function updateCloseItems(){  var browser = getBrowser();  if (browser && browser.getStripVisibility()) {    document.getElementById('menu_closeOtherTabs').hidden = false;    if (browser.tabContainer.childNodes.length > 1) {      document.getElementById('menu_close').setAttribute('label', gNavigatorBundle.getString('tabs.closeTab'));      document.getElementById('cmd_closeOtherTabs').removeAttribute('disabled');      document.getElementById('menu_closeWindow').hidden = false;    }    else {      document.getElementById('menu_close').setAttribute('label', gNavigatorBundle.getString('tabs.close'));      document.getElementById('cmd_closeOtherTabs').setAttribute('disabled', 'true');      document.getElementById('menu_closeWindow').hidden = true;    }  } else {    document.getElementById('menu_close').setAttribute('label', gNavigatorBundle.getString('tabs.close'));    document.getElementById('menu_closeWindow').hidden = true;    document.getElementById('menu_closeOtherTabs').hidden = true;  }  var recentTabsItem = document.getElementById("menu_recentTabs");  recentTabsItem.setAttribute("disabled", browser.getUndoList().length == 0);}
meta: 10234	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/10234/929a961de54c32b2c5ea3db3308d338dc0d8274b/navigator.js/buggy/suite/browser/navigator.js