function updateTabContextMenu(tab) {
  let menu = document.getElementById("tabContextMenu");
  if (!tab)
    tab = gBrowser.selectedTab;
  var evt = new Event("");
  tab.dispatchEvent(evt);
  menu.openPopup(tab, "end_after", 0, 0, true, false, evt);
  is(TabContextMenu.contextTab, tab, "TabContextMenu context is the expected tab");
  menu.hidePopup();
}