Bug 1501789 - Use the JSM global to create permanentKeys to avoid leaking windows after tab tear out / adoption. r=Felipe

Differential Revision: https://phabricator.services.mozilla.com/D9975

--HG--
extra : moz-landing-system : lando

browser/base/content/tabbrowser.js

@@ -1815,7 +1815,10 @@ window._gBrowser = {
     userContextId,
   } = {}) {
     let b = document.createXULElement("browser");
-    b.permanentKey = {};
+    // Use the JSM global to create the permanentKey, so that if the
+    // permanentKey is held by something after this window closes, it
+    // doesn't keep the window alive.
+    b.permanentKey = new (Cu.getGlobalForObject(Services).Object);
 
     const defaultBrowserAttributes = {
       contextmenu: "contentAreaContextMenu",

browser/base/content/test/performance/browser.ini

@@ -25,7 +25,6 @@ run-if = debug || devedition || nightly_build # Requires startupRecorder.js, whi
 [browser_tabclose.js]
 skip-if = (os == 'win' && bits == 32) # Bug 1488537
 [browser_tabdetach.js]
-skip-if = debug # Bug 1501789
 [browser_tabopen.js]
 skip-if = (verify && (os == 'mac'))
 [browser_tabopen_squeeze.js]