diff --git a/toolkit/components/extensions/Extension.jsm b/toolkit/components/extensions/Extension.jsm
index 64fef9124330..5279267796ef 100644
--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -614,7 +614,7 @@ GlobalManager = {
 
   init(extension) {
     if (this.extensionMap.size == 0) {
-      Services.obs.addObserver(this, "content-document-global-created", false);
+      Services.obs.addObserver(this, "document-element-inserted", false);
       UninstallObserver.init();
       this.initialized = true;
     }
@@ -626,7 +626,7 @@ GlobalManager = {
     this.extensionMap.delete(extension.id);
 
     if (this.extensionMap.size == 0 && this.initialized) {
-      Services.obs.removeObserver(this, "content-document-global-created");
+      Services.obs.removeObserver(this, "document-element-inserted");
       this.initialized = false;
     }
   },
@@ -712,7 +712,12 @@ GlobalManager = {
     Schemas.inject(dest, schemaWrapper);
   },
 
-  observe(contentWindow, topic, data) {
+  observe(document, topic, data) {
+    let contentWindow = document.defaultView;
+    if (!contentWindow) {
+      return;
+    }
+
     let inject = (extension, context) => {
       // We create two separate sets of bindings, one for the `chrome`
       // global, and one for the `browser` global. The latter returns
@@ -741,7 +746,6 @@ GlobalManager = {
       return;
     }
 
-
     let docShell = contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
                                 .getInterface(Ci.nsIDocShell);
 
@@ -765,9 +769,8 @@ GlobalManager = {
       type = "popup";
     }
 
-
     let extension = this.extensionMap.get(id);
-    let uri = contentWindow.document.documentURIObject;
+    let uri = document.documentURIObject;
     let incognito = PrivateBrowsingUtils.isContentWindowPrivate(contentWindow);
 
     let context = new ExtensionContext(extension, {type, contentWindow, uri, docShell, incognito});
diff --git a/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html b/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html
index b7859b6d4dc6..777f9944e04b 100644
--- a/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html
+++ b/toolkit/components/extensions/test/mochitest/test_ext_tab_teardown.html
@@ -14,7 +14,7 @@
 "use strict";
 
 // Test for tabs opened using tabs.create and window.open
-function* runTabReloadAndCloseTest({extension, isInitiallyBlankUrl}) {
+function* runTabReloadAndCloseTest(extension) {
   let chromeScript = SpecialPowers.loadChromeScript(
       SimpleTest.getTestFileURL("file_teardown_test.js"));
   yield chromeScript.promiseOneMessage("chromescript-startup");
@@ -37,17 +37,8 @@ function* runTabReloadAndCloseTest({extension, isInitiallyBlankUrl}) {
   extension.sendMessage("reload extension page");
   let extensionPageUrl2 = yield extension.awaitMessage("extension page loaded");
 
-  // When the tab is opened with window.open, the initial URL happens to be
-  // about:blank.
-  if (isInitiallyBlankUrl) {
-    is(extensionPageUrl, "about:blank",
-        "The tab URL before reload should be about:blank");
-    isnot(extensionPageUrl, extensionPageUrl2,
-        "After a page reload the tab URL shouldn't be blank.");
-  } else {
-    is(extensionPageUrl, extensionPageUrl2,
-        "The tab's URL is expected to not change after a page reload");
-  }
+  is(extensionPageUrl, extensionPageUrl2,
+      "The tab's URL is expected to not change after a page reload");
 
   contextEvents = yield* getContextEvents();
   is(contextEvents.length, 2, "ExtensionContext change after tab reload");
@@ -105,7 +96,7 @@ add_task(function* test_extension_page_tabs_create_reload_and_close() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
 
-  yield* runTabReloadAndCloseTest({extension});
+  yield* runTabReloadAndCloseTest(extension);
 });
 
 add_task(function* test_extension_page_window_open_reload_and_close() {
@@ -136,16 +127,7 @@ add_task(function* test_extension_page_window_open_reload_and_close() {
   }
 
   function pageScript() {
-    if (performance.navigation.type === 0) { // TYPE_NAVIGATION
-      // The ExtensionContext URL happens to be "about:blank" when the page is
-      // loaded via window.open().
-      browser.test.sendMessage("extension page loaded", "about:blank");
-    } else if (performance.navigation.type === 1) { // TYPE_RELOAD
-      browser.test.sendMessage("extension page loaded", document.URL);
-    } else {
-      browser.test.notifyFail(
-          "Unexpected navigation type: " + performance.navigation.type);
-    }
+    browser.test.sendMessage("extension page loaded", document.URL);
   }
 
   let extensionData = {
@@ -160,7 +142,7 @@ add_task(function* test_extension_page_window_open_reload_and_close() {
   let extension = ExtensionTestUtils.loadExtension(extensionData);
   yield extension.startup();
   yield extension.awaitMessage("setup-intermediate-tab");
-  yield* runTabReloadAndCloseTest({extension, isInitiallyBlankUrl: true});
+  yield* runTabReloadAndCloseTest(extension);
 });
 </script>