The Tor Browser / file revision

 'use strict';

 const { Ci } = require('chrome');

 const { openTab, closeTab } = require('sdk/tabs/utils');

 const { browserWindows } = require('sdk/windows');

 const { getOwnerWindow } = require('sdk/private-browsing/window/utils');

 const { isPrivate } = require('sdk/private-browsing');

 exports.testIsPrivateOnTab = function(assert) {

   let window = browserWindows.activeWindow;

   let chromeWindow = getOwnerWindow(window);

   assert.ok(chromeWindow instanceof Ci.nsIDOMWindow, 'associated window is found');

   assert.ok(!isPrivate(chromeWindow), 'the top level window is not private');

   let rawTab = openTab(chromeWindow, 'data:text/html,<h1>Hi!</h1>', {

     isPrivate: true

   });

   // test that the tab is private

   assert.ok(rawTab.browser.docShell.QueryInterface(Ci.nsILoadContext).usePrivateBrowsing);

   assert.ok(isPrivate(rawTab.browser.contentWindow));

   assert.ok(isPrivate(rawTab.browser));

   closeTab(rawTab);

 };