>>607
function _f(event) {
if (event.target.localName == 'tabs' && event.button == 2){
var undoPopup = document.getElementById("myUndoPopup");
if(!undoPopup){
undoPopup = document.createElement("menupopup");
undoPopup.setAttribute("id","myUndoPopup");
var mainPopupSet = document.getElementById("mainPopupSet");
mainPopupSet.appendChild(undoPopup);
}
while (undoPopup.hasChildNodes())
undoPopup.removeChild(undoPopup.firstChild);
let tabsFragment = RecentlyClosedTabsAndWindowsMenuUtils.getTabsFragment(window, "menuitem");
undoPopup.appendChild(tabsFragment);
undoPopup.openPopupAtScreen(event.screenX, event.screenY, true);
event.stopPropagation();
event.preventDefault();
setTimeout(function(){document.getElementById("toolbar-context-menu").hidePopup();}, 0);//←ここに追加でどう？
}
}
gBrowser.mTabContainer.addEventListener('click', _f, false);