diff --git a/testing/mochitest/browser-test.js b/testing/mochitest/browser-test.js
index 4d48bcf9717e..dd9982f3000c 100644
--- a/testing/mochitest/browser-test.js
+++ b/testing/mochitest/browser-test.js
@@ -129,8 +129,6 @@ function Tester(aTests, structuredLogger, aCallback) {
   this.structuredLogger = structuredLogger;
   this.tests = aTests;
   this.callback = aCallback;
-  this.openedWindows = {};
-  this.openedURLs = {};
 
   this._scriptLoader = Services.scriptloader;
   this.EventUtils = {};
@@ -164,13 +162,6 @@ function Tester(aTests, structuredLogger, aCallback) {
   this.Promise = Components.utils.import("resource://gre/modules/Promise.jsm", null).Promise;
   this.Assert = Components.utils.import("resource://testing-common/Assert.jsm", null).Assert;
 
-  Services.ppmm.loadProcessScript("chrome://mochikit/content/document-observer-script.js", true);
-  Services.ppmm.addMessageListener("browser-test:documentCreated", (msg) => {
-    if (this.currentTest) {
-      this.onDocumentCreated(msg.data);
-    }
-  });
-
   this.SimpleTestOriginal = {};
   SIMPLETEST_OVERRIDES.forEach(m => {
     this.SimpleTestOriginal[m] = this.SimpleTest[m];
@@ -222,7 +213,6 @@ Tester.prototype = {
   checker: null,
   currentTestIndex: -1,
   lastStartTime: null,
-  openedWindows: null,
   lastAssertionCount: 0,
   failuresFromInitialWindowState: 0,
 
@@ -374,7 +364,6 @@ Tester.prototype = {
     } else {
       TabDestroyObserver.destroy();
       Services.console.unregisterListener(this);
-      Services.ppmm.broadcastAsyncMessage("browser-test:removeObservers", {});
       this.Promise.Debugging.clearUncaughtErrorObservers();
       this._treatUncaughtRejectionsAsFailures = false;
 
@@ -403,7 +392,6 @@ Tester.prototype = {
       this.callback(this.tests);
       this.callback = null;
       this.tests = null;
-      this.openedWindows = null;
     }
   },
 
@@ -419,16 +407,6 @@ Tester.prototype = {
     }
   },
 
-  onDocumentCreated: function Tester_onDocumentCreated({ location, outerID, innerID }) {
-    if (!(outerID in this.openedWindows)) {
-      this.openedWindows[outerID] = this.currentTest;
-    }
-    this.openedWindows[innerID] = this.currentTest;
-
-    let url = location || "about:blank";
-    this.openedURLs[outerID] = this.openedURLs[innerID] = url;
-  },
-
   onConsoleMessage: function Tester_onConsoleMessage(aConsoleMessage) {
     // Ignore empty messages.
     if (!aConsoleMessage.message)
diff --git a/testing/mochitest/document-observer-script.js b/testing/mochitest/document-observer-script.js
deleted file mode 100644
index 55e20aca3b33..000000000000
--- a/testing/mochitest/document-observer-script.js
+++ /dev/null
@@ -1,30 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this file,
- * You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-let { interfaces: Ci, utils: Cu } = Components;
-
-Cu.import("resource://gre/modules/Services.jsm");
-
-let observer = {
-  observe(aWindow) {
-    let utils = aWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-                       .getInterface(Ci.nsIDOMWindowUtils);
-    let outerID = utils.outerWindowID;
-    let innerID = utils.currentInnerWindowID;
-
-    // NB: We don't have to distinguish between whether this is for a chrome
-    // or content document.
-    sendAsyncMessage("browser-test:documentCreated",
-                     { location: aWindow.location.href,
-                       outerID, innerID });
-  },
-};
-
-addMessageListener("browser-test:removeObservers", (msg) => {
-  Services.obs.removeObserver(observer, "chrome-document-global-created");
-  Services.obs.removeObserver(observer, "content-document-global-created");
-});
-
-Services.obs.addObserver(observer, "chrome-document-global-created", false);
-Services.obs.addObserver(observer, "content-document-global-created", false);
diff --git a/testing/mochitest/jar.mn b/testing/mochitest/jar.mn
index fa8fa98403e2..7646ec7e4c22 100644
--- a/testing/mochitest/jar.mn
+++ b/testing/mochitest/jar.mn
@@ -11,7 +11,6 @@ mochikit.jar:
   content/mochitest-e10s-utils.js (mochitest-e10s-utils.js)
   content/shutdown-leaks-collector.js (shutdown-leaks-collector.js)
   content/ShutdownLeaksCollector.jsm (ShutdownLeaksCollector.jsm)
-  content/document-observer-script.js (document-observer-script.js)
   content/harness.xul (harness.xul)
   content/redirect.html (redirect.html)
   content/server.js (server.js)