--- a/browser/extensions/formautofill/moz.build
+++ b/browser/extensions/formautofill/moz.build
@@ -10,17 +10,13 @@ DEFINES['MOZ_APP_MAXVERSION'] = CONFIG['
 FINAL_TARGET_FILES.features['formautofill@mozilla.org'] += [
   'bootstrap.js'
 ]
 
 FINAL_TARGET_PP_FILES.features['formautofill@mozilla.org'] += [
   'install.rdf.in'
 ]
 
-TESTING_JS_MODULES += [
-  'test/unit/MockDocument.jsm'
-]
-
 BROWSER_CHROME_MANIFESTS += ['test/browser/browser.ini']
 
 XPCSHELL_TESTS_MANIFESTS += ['test/unit/xpcshell.ini']
 
 JAR_MANIFESTS += ['jar.mn']

rename from browser/extensions/formautofill/test/unit/MockDocument.jsm
rename to testing/modules/MockDocument.jsm

--- a/toolkit/components/passwordmgr/test/unit/head.js
+++ b/toolkit/components/passwordmgr/test/unit/head.js
@@ -92,54 +92,16 @@ function getTempFile(aLeafName)
 ////////////////////////////////////////////////////////////////////////////////
 
 const RecipeHelpers = {
   initNewParent() {
     return (new LoginRecipesParent({ defaults: null })).initializationPromise;
   },
 };
 
-const MockDocument = {
-  /**
-   * Create a document for the given URL containing the given HTML with the ownerDocument of all <form>s having a mocked location.
-   */
-  createTestDocument(aDocumentURL, aContent = "<form>", aType = "text/html") {
-    let parser = Cc["@mozilla.org/xmlextras/domparser;1"].
-                 createInstance(Ci.nsIDOMParser);
-    parser.init();
-    let parsedDoc = parser.parseFromString(aContent, aType);
-
-    for (let element of parsedDoc.forms) {
-      this.mockOwnerDocumentProperty(element, parsedDoc, aDocumentURL);
-    }
-    return parsedDoc;
-  },
-
-  mockOwnerDocumentProperty(aElement, aDoc, aURL) {
-    // Mock the document.location object so we can unit test without a frame. We use a proxy
-    // instead of just assigning to the property since it's not configurable or writable.
-    let document = new Proxy(aDoc, {
-      get(target, property, receiver) {
-        // document.location is normally null when a document is outside of a "browsing context".
-        // See https://html.spec.whatwg.org/#the-location-interface
-        if (property == "location") {
-          return new URL(aURL);
-        }
-        return target[property];
-      },
-    });
-
-    // Assign element.ownerDocument to the proxy so document.location works.
-    Object.defineProperty(aElement, "ownerDocument", {
-      value: document,
-    });
-  },
-
-};
-
 //// Initialization functions common to all tests
 
 add_task(function* test_common_initialize()
 {
   // Before initializing the service for the first time, we should copy the key
   // file required to decrypt the logins contained in the SQLite databases used
   // by migration tests.  This file is not required for the other tests.
   yield OS.File.copy(do_get_file("data/key3.db").path,

--- a/toolkit/components/passwordmgr/test/unit/test_context_menu.js
+++ b/toolkit/components/passwordmgr/test/unit/test_context_menu.js
@@ -1,16 +1,17 @@
 /*
  * Test the password manager context menu.
  */
 
 "use strict";
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/LoginManagerContextMenu.jsm");
+Cu.import("resource://testing-common/MockDocument.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "_stringBundle", function() {
   return Services.strings.
          createBundle("chrome://passwordmgr/locale/passwordmgr.properties");
 });
 
 /**
  * Prepare data for the following tests.

--- a/toolkit/components/passwordmgr/test/unit/test_getFormFields.js
+++ b/toolkit/components/passwordmgr/test/unit/test_getFormFields.js
@@ -2,16 +2,17 @@
  * Test for LoginManagerContent._getFormFields.
  */
 
 "use strict";
 
 //Services.prefs.setBoolPref("signon.debug", true);
 
 Cu.importGlobalProperties(["URL"]);
+Cu.import("resource://testing-common/MockDocument.jsm");
 
 const LMCBackstagePass = Cu.import("resource://gre/modules/LoginManagerContent.jsm");
 const { LoginManagerContent, FormLikeFactory } = LMCBackstagePass;
 const TESTCASES = [
   {
     description: "1 password field outside of a <form>",
     document: `<input id="pw1" type=password>`,
     returnedFieldIDs: [null, "pw1", null],

--- a/toolkit/components/passwordmgr/test/unit/test_getPasswordFields.js
+++ b/toolkit/components/passwordmgr/test/unit/test_getPasswordFields.js
@@ -1,14 +1,15 @@
 /*
  * Test for LoginManagerContent._getPasswordFields using FormLikeFactory.
  */
 
 "use strict";
 
+Cu.import("resource://testing-common/MockDocument.jsm");
 const LMCBackstagePass = Cu.import("resource://gre/modules/LoginManagerContent.jsm");
 const { LoginManagerContent, FormLikeFactory } = LMCBackstagePass;
 const TESTCASES = [
   {
     description: "Empty document",
     document: ``,
     returnedFieldIDsByFormLike: [],
     skipEmptyFields: undefined,

--- a/toolkit/components/passwordmgr/test/unit/test_recipes_content.js
+++ b/toolkit/components/passwordmgr/test/unit/test_recipes_content.js
@@ -2,16 +2,17 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 /**
  * Test filtering recipes in LoginRecipesContent.
  */
 
 "use strict";
 
+Cu.import("resource://testing-common/MockDocument.jsm");
 Cu.importGlobalProperties(["URL"]);
 
 add_task(function* test_getFieldOverrides() {
   let recipes = new Set([
     { // path doesn't match but otherwise good
       hosts: ["example.com:8080"],
       passwordSelector: "#password",
       pathRegex: /^\/$/,

copy from browser/extensions/formautofill/test/unit/MockDocument.jsm
copy to toolkit/modules/MockDocument.jsm

--- a/toolkit/modules/moz.build
+++ b/toolkit/modules/moz.build
@@ -5,16 +5,17 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 XPCSHELL_TESTS_MANIFESTS += ['tests/xpcshell/xpcshell.ini']
 BROWSER_CHROME_MANIFESTS += ['tests/browser/browser.ini']
 MOCHITEST_MANIFESTS += ['tests/mochitest/mochitest.ini']
 MOCHITEST_CHROME_MANIFESTS += ['tests/chrome/chrome.ini']
 
 TESTING_JS_MODULES += [
+    'MockDocument.jsm',
     'tests/PromiseTestUtils.jsm',
     'tests/xpcshell/TestIntegration.jsm',
 ]
 
 SPHINX_TREES['toolkit_modules'] = 'docs'
 
 EXTRA_JS_MODULES += [
     'addons/MatchPattern.jsm',