--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -6659,18 +6659,18 @@ var gIdentityHandler = {
     delete this._identityPopup;
     return this._identityPopup = document.getElementById("identity-popup");
   },
   get _identityBox() {
     delete this._identityBox;
     return this._identityBox = document.getElementById("identity-box");
   },
   get _identityPopupMultiView() {
-    delete _identityPopupMultiView;
-    return document.getElementById("identity-popup-multiView");
+    delete this._identityPopupMultiView;
+    return this._identityPopupMultiView = document.getElementById("identity-popup-multiView");
   },
   get _identityPopupContentHosts() {
     delete this._identityPopupContentHosts;
     let selector = ".identity-popup-headline.host";
     return this._identityPopupContentHosts = [
       ...this._identityPopupMultiView._mainView.querySelectorAll(selector),
       ...document.querySelectorAll(selector)
     ];

--- a/toolkit/.eslintrc.js
+++ b/toolkit/.eslintrc.js
@@ -58,16 +58,19 @@ module.exports = {
     // "new-parens": "error",
 
     // Use [] instead of Array()
     // "no-array-constructor": "error",
 
     // Disallow the use of debugger
     "no-debugger": "error",
 
+    // Disallow deleting variables
+    "no-delete-var": "error",
+
     // No duplicate arguments in function declarations
     "no-dupe-args": "error",
 
     // No duplicate keys in object declarations
     "no-dupe-keys": "error",
 
     // No duplicate cases in switch statements
     "no-duplicate-case": "error",