--- a/toolkit/components/passwordmgr/LoginManagerParent.jsm
+++ b/toolkit/components/passwordmgr/LoginManagerParent.jsm
@@ -4,16 +4,22 @@
 
 "use strict";
 
 const { XPCOMUtils } = ChromeUtils.import(
   "resource://gre/modules/XPCOMUtils.jsm"
 );
 const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
 
+const LoginInfo = new Components.Constructor(
+  "@mozilla.org/login-manager/loginInfo;1",
+  Ci.nsILoginInfo,
+  "init"
+);
+
 XPCOMUtils.defineLazyGlobalGetters(this, ["URL"]);
 
 ChromeUtils.defineModuleGetter(
   this,
   "AutoCompletePopup",
   "resource://gre/modules/AutoCompletePopup.jsm"
 );
 ChromeUtils.defineModuleGetter(
@@ -518,20 +524,17 @@ this.LoginManagerParent = {
       Services.logins.modifyLogin(login, propBag);
     }
 
     if (!Services.logins.getLoginSavingEnabled(origin)) {
       log("(form submission ignored -- saving is disabled for:", origin, ")");
       return;
     }
 
-    let formLogin = Cc["@mozilla.org/login-manager/loginInfo;1"].createInstance(
-      Ci.nsILoginInfo
-    );
-    formLogin.init(
+    let formLogin = new LoginInfo(
       origin,
       formActionOrigin,
       null,
       usernameField ? usernameField.value : "",
       newPasswordField.value,
       usernameField ? usernameField.name : "",
       newPasswordField.name
     );
@@ -696,20 +699,33 @@ this.LoginManagerParent = {
       log("_onGeneratedPasswordFilledOrEdited: The password field is empty");
       return;
     }
     if (passwordInField != password) {
       // The user edited the field after generation to a non-empty value.
       log("The field containing the generated password has changed");
       return;
     }
-    let formLogin = Cc["@mozilla.org/login-manager/loginInfo;1"].createInstance(
-      Ci.nsILoginInfo
+
+    let formLogin = new LoginInfo(
+      formOrigin,
+      formActionOrigin,
+      null,
+      username,
+      password
     );
-    formLogin.init(formOrigin, formActionOrigin, null, username, password);
+
+    let formLoginWithoutUsername = new LoginInfo(
+      formOrigin,
+      formActionOrigin,
+      null,
+      "",
+      password
+    );
+
     let shouldSaveLogin = true;
 
     // This will throw if we can't look up the entry in the password/origin map
     if (!generatedPW.filled) {
       // record first use of this generated password
       Services.telemetry.recordEvent(
         "pwmgr",
         "autocomplete_field",
@@ -737,40 +753,40 @@ this.LoginManagerParent = {
     });
 
     if (logins.length > 0) {
       log(
         "_onGeneratedPasswordFilledOrEdited: Login already saved for this site"
       );
       shouldSaveLogin = false;
       for (let login of logins) {
-        if (formLogin.matches(login, false)) {
+        if (formLoginWithoutUsername.matches(login, false)) {
           // This login is already saved so show no new UI.
           log(
             "_onGeneratedPasswordFilledOrEdited: Matching login already saved"
           );
           return;
         }
       }
     }
 
     if (shouldSaveLogin) {
-      Services.logins.addLogin(formLogin);
+      Services.logins.addLogin(formLoginWithoutUsername);
     }
     log(
       "_onGeneratedPasswordFilledOrEdited: show dismissed save-password notification"
     );
     let browser = browsingContext.top.embedderElement;
     let prompter = this._getPrompter(browser, openerTopWindowID);
 
     if (shouldSaveLogin) {
       // If we auto-saved the login then show a change doorhanger to allow
       // modifying it e.g. adding a username.
       prompter.promptToChangePassword(
-        formLogin,
+        formLoginWithoutUsername,
         formLogin,
         true, // dimissed prompt
         shouldSaveLogin // notifySaved
       );
       return;
     }
     prompter.promptToSavePassword(
       formLogin,

--- a/toolkit/components/passwordmgr/test/browser/browser_generated_password_doorhangers.js
+++ b/toolkit/components/passwordmgr/test/browser/browser_generated_password_doorhangers.js
@@ -133,16 +133,21 @@ add_task(async function autocomplete_gen
           // We'll reuse the form_basic.html, but ensure we'll get the generated password autocomplete option
           passwordInput.setAttribute("autocomplete", "new-password");
           passwordInput.value = "";
           let usernameInput = content.document.querySelector(usernameSelector);
           usernameInput.setUserInput("user1");
         }
       );
 
+      let storageChangedPromise = TestUtils.topicObserved(
+        "passwordmgr-storage-changed",
+        (_, data) => data == "addLogin"
+      );
+
       let confirmationHint = document.getElementById("confirmation-hint");
       let hintPromiseShown = BrowserTestUtils.waitForEvent(
         confirmationHint,
         "popupshown"
       );
       await fillGeneratedPasswordFromACPopup(browser, passwordInputSelector);
       await ContentTask.spawn(
         browser,
@@ -152,31 +157,36 @@ add_task(async function autocomplete_gen
           is(
             passwordInput.value.length,
             15,
             "Password field was filled with generated password"
           );
         }
       );
 
+      let [{ username, password }] = await storageChangedPromise;
       // Make sure confirmation hint was shown
       await hintPromiseShown;
 
       Assert.equal(
         confirmationHint.anchorNode.id,
         "password-notification-icon",
         "Hint should be anchored on the password notification icon"
       );
 
       let hintPromiseHidden = BrowserTestUtils.waitForEvent(
         confirmationHint,
         "popuphidden"
       );
       await hintPromiseHidden;
 
+      // Check properties of the newly auto-saved login
+      is(username, "", "Saved login should have no username");
+      is(password.length, 15, "Saved login should have generated password");
+
       // check a dismissed prompt was shown with extraAttr attribute
       let notif = getCaptureDoorhanger("password-change");
       ok(notif && notif.dismissed, "Dismissed notification was created");
       is(
         notif.anchorElement.getAttribute("extraAttr"),
         "attention",
         "Check if icon has the extraAttr attribute"
       );