diff --git a/toolkit/components/passwordmgr/test/mochitest/test_autocomplete_basic_form_subdomain.html b/toolkit/components/passwordmgr/test/mochitest/test_autocomplete_basic_form_subdomain.html
--- a/toolkit/components/passwordmgr/test/mochitest/test_autocomplete_basic_form_subdomain.html
+++ b/toolkit/components/passwordmgr/test/mochitest/test_autocomplete_basic_form_subdomain.html
@@ -12,42 +12,34 @@
 <body>
 Login Manager test: logins with non-exact match origin appear in autocomplete dropdown
 <p id="display"></p>
 
 <!-- we presumably can't hide the content for this test. -->
-<div id="content"></div>
+<div id="content">
+
+  <!-- form1 tests multiple matching logins -->
+  <form id="form1" action="https://otherexample.com/formtest.js" onsubmit="return false;">
+    <input  type="text"       name="uname">
+    <input  type="password"   name="pword">
+    <button type="submit">Submit</button>
+  </form>
+</div>
 <pre id="test">
 <script class="testbody" type="text/javascript">
-function createForm () {
-  const form = document.createElement("form");
-  form.action = "https://otherexample.com/formtest.js"
 
-  const usernameInput = document.createElement("input");
-  usernameInput.type = "text";
-  usernameInput.name = "uname";
-  form.appendChild(usernameInput);
-
-  const passwordInput = document.createElement("input");
-  passwordInput.type = "password";
-  passwordInput.name = "pword";
-  form.appendChild(passwordInput);
+const uname = getFormElementByName(1, "uname");
+const pword = getFormElementByName(1, "pword");
 
-  const submitButton = document.createElement("button");
-  submitButton.type = "submit";
-  submitButton.name = "submit";
-  submitButton.innerText = "Submit";
-  form.appendChild(submitButton);
-
-  const content = document.getElementById("content");
+// Restore the form to the default state.
+function restoreForm() {
+  uname.value = "";
+  pword.value = "";
+  uname.focus();
+}
 
-  if (content.firstChild) {
-    content.replaceChild(form, content.firstChild);
-  } else {
-    content.appendChild(form);
-  }
-
-  return form;
+function spinEventLoop() {
+  return Promise.resolve();
 }
 
 const setupScript = runInParent(function setup() {
   addMessageListener("getDateString", () => {
     const dateAndTimeFormatter = new Services.intl.DateTimeFormat(undefined, { dateStyle: "medium" });
@@ -83,28 +75,26 @@
   });
   listenForUnexpectedPopupShown();
 });
 
 add_task(async function test_form1_initial_empty() {
-  const form = createForm();
+  await SimpleTest.promiseFocus(window);
 
   // Make sure initial form is empty.
-  checkLoginForm(form.uname, "", form.pword, "");
+  checkLoginForm(uname, "", pword, "");
   const popupState = await getPopupState();
   is(popupState.open, false, "Check popup is initially closed");
 });
 
 /* For this testcase, there exists two logins for this origin
  * on different subdomains but with different passwords. Both logins
  * should appear in the autocomplete popup.
  */
 add_task(async function test_form1_menu_shows_two_logins_same_usernames_for_different_subdomain() {
-  const form = createForm();
-
+  await SimpleTest.promiseFocus(window);
   // Trigger autocomplete popup
-  form.uname.focus();
-
+  restoreForm();
   const autocompleteItems = await popupByArrowDown();
 
   const popupState = await getPopupState();
   is(popupState.selectedIndex, -1, "Check no entries are selected upon opening");
 
@@ -114,31 +104,29 @@
   const username = `dsdu1 (${dateString})`;
 
   checkAutoCompleteResults(autocompleteItems, [username, username], window.location.host, "Check all menuitems are displayed correctly.");
 
   synthesizeKey("KEY_ArrowDown"); // first item
-  checkLoginForm(form.uname, "", form.pword, ""); // value shouldn't update just by selecting
+  checkLoginForm(uname, "", pword, ""); // value shouldn't update just by selecting
 
   synthesizeKey("KEY_Enter");
   await promiseFormsProcessedInSameProcess();
-  is(form.pword.value, "dsdp1", "password should match the login that was selected");
-  checkLoginForm(form.uname, "dsdu1", form.pword, "dsdp1");
+  is(pword.value, "dsdp1", "password should match the login that was selected");
+  checkLoginForm(uname, "dsdu1", pword, "dsdp1");
 
-  form.uname.value = "";
-  form.pword.value = "";
-  form.uname.focus();
+  restoreForm();
 
   await popupByArrowDown();
 
   synthesizeKey("KEY_ArrowDown"); // first item
   synthesizeKey("KEY_ArrowDown"); // second item
-  checkLoginForm(form.uname, "", form.pword, ""); // value shouldn't update just by selecting
+  checkLoginForm(uname, "", pword, ""); // value shouldn't update just by selecting
 
   synthesizeKey("KEY_Enter");
   await promiseFormsProcessedInSameProcess();
-  is(form.pword.value, "dsdp1prime", "Password should match the login that was selected");
-  checkLoginForm(form.uname, "dsdu1", form.pword, "dsdp1prime");
+  is(pword.value, "dsdp1prime", "Password should match the login that was selected");
+  checkLoginForm(uname, "dsdu1", pword, "dsdp1prime");
 });
 </script>
 </pre>
 </body>
 </html>