Bug 1572109: Fix tabbing in edit mode. r=jaws

Differential Revision: https://phabricator.services.mozilla.com/D44056

--HG--
extra : moz-landing-system : lando

browser/components/aboutlogins/content/components/login-list.js

@@ -427,7 +427,15 @@ export default class LoginList extends HTMLElement {
       let loginItem = document.querySelector("login-item");
       if (loginItem) {
         event.preventDefault();
-        loginItem.shadowRoot.querySelector(".edit-button").focus();
+        let editButton = loginItem.shadowRoot.querySelector(".edit-button");
+        if (editButton && !editButton.disabled) {
+          editButton.focus();
+          return;
+        }
+        let deleteButton = loginItem.shadowRoot.querySelector(
+          "button.delete-button"
+        );
+        deleteButton.focus();
       }
       return;
     } else if (this._list != this.shadowRoot.activeElement) {