From 2c5248df9389b142085bd85f9811b0ef0847d1c8 Mon Sep 17 00:00:00 2001
From: Kathy Brade <brade@pearlcrescent.com>
Date: Thu, 3 Oct 2019 10:05:33 -0400
Subject: [PATCH] Bug 31955: On macOS avoid throwing inside
 nonBrowserWindowStartup()

Inside nonBrowserWindowStartup(), do not assume that XUL elements
that are only part of the Mac hidden window are available in all
non-browser windows.
---
 browser/base/content/nonbrowser-mac.js | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/browser/base/content/nonbrowser-mac.js b/browser/base/content/nonbrowser-mac.js
index 44f5cfd03127c..a7174a9295d08 100644
--- a/browser/base/content/nonbrowser-mac.js
+++ b/browser/base/content/nonbrowser-mac.js
@@ -102,10 +102,17 @@ function nonBrowserWindowStartup() {
   }
 
   if (PrivateBrowsingUtils.permanentPrivateBrowsing) {
-    document.getElementById("macDockMenuNewWindow").hidden = true;
+    element = document.getElementById("macDockMenuNewWindow");
+    if (element) {
+      element.hidden = true;
+    }
   }
+
   if (!PrivateBrowsingUtils.enabled) {
-    document.getElementById("macDockMenuNewPrivateWindow").hidden = true;
+    element = document.getElementById("macDockMenuNewPrivateWindow");
+    if (element) {
+      element.hidden = true;
+    }
   }
 
   delayedStartupTimeoutId = setTimeout(nonBrowserWindowDelayedStartup, 0);
-- 
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