// http://lxr.mozilla.org/mozilla1.8/source/browser/base/content/browser.js#1944
BrowserCloseTabOrWindow = function()
{
  if (gBrowser.localName == "tabbrowser" &&
      gBrowser.tabContainer.childNodes.length > 1) {
    // Just close up a tab.
    gBrowser.removeCurrentTab();
    return;
  }

  BrowserCloseWindow();
}

//eval('gBrowser.removeTab = ' + gBrowser.removeTab.toString().replace('if (l == 1', 'if (l == 1) { window.close(); return; } if (l == 1'));