From bdba39afd2b0cf44e924b85555bcfa061f9c8f8a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A1n=20Jockusch?= <jan.jockusch@perfact.de>
Date: Wed, 8 May 2019 07:21:19 +0200
Subject: [PATCH] Same source issue solved. fullscreenToggle now checks if it
 is permitted to inspect other iframes.

---
 app/ui.js | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/app/ui.js b/app/ui.js
index 91bd2d3a..d90025ed 100644
--- a/app/ui.js
+++ b/app/ui.js
@@ -1198,13 +1198,17 @@ const UI = {
             let doc_el = document.documentElement;
             if (window.self !== window.top) {
                 // Seek out the correct iframe from the parent document.
-                // This will produce errors if the iframe does not come from
-                // the same origin, so it is advisable to put the viewer in
-                // iframes only if you are on the same server.
                 let iframes = window.parent.document
                     .getElementsByTagName('iframe');
                 for (let i in iframes) {
-                    if (iframes[i].contentDocument === document) {
+                    let content_doc = null;
+                    try {
+                        content_doc = iframes[i].contentDocument;
+                    } catch (err) {
+                        // I may not be permitted to read the contentDocument
+                        // of the iframe, but then it can't be me, so ignore.
+                    }
+                    if (content_doc === document) {
                         doc_el = iframes[i];
                         // To use .body.msRequestFullscreen in IE, we need to
                         // set the document element accordingly.