diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index a7ae519ece24..63cd79a62203 100755
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -6664,8 +6664,8 @@ var gIdentityHandler = {
     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;
diff --git a/toolkit/.eslintrc.js b/toolkit/.eslintrc.js
index bc041c7906bf..c3e345d295be 100644
--- a/toolkit/.eslintrc.js
+++ b/toolkit/.eslintrc.js
@@ -66,6 +66,9 @@ module.exports = {
     // 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",