This one really caught me by surprise! I have an internal Django database system. Staff typically use Firefox or Chrome to access it from Linux or Windows machines. As part of this system, it uses Grappelli library which in turn uses TinyMCE V3.5.8. Specifically, in a text box TinyMCE provides advanced editing and fonting. Allows the user to embed links or images. This system was working fine on Django 2.2. My provider (Python Anywhere) retired the server image I was running on, so I updated everything to Django 4.2 on their latest "haggis" system image. Everything seemed to transfer over without any errors - at first. In fact, it was a week later somebody tried to change a font colour by clicking the popup button that opens a colour picker. That pop up looks blank! (its not, the HTML is there but without the custom CSS nothing is visible) In developer mode on Firefox or Chrome I can see what the problem is: The popup is disconnected from the parent. The parents CSS and classes - specifically tinyMCE - is not present. So its missing the styling and JS to operate. One of the first things the popup JS does is copy in the tinyMCE and tinymce classes from the parent. But they are not there, in fact .opener is null and .parent is stripped down. What is really weird is on my test server, where I tested everything before updating the live server, it works! The test server uses Django's "runserver" to run a very simple (unsecure) http server just to test code. Whereas the live server is locked on HTTPS. What confuses me is I don't see any console log messages that would indicate the browser decided to "protect" me. How can I figure out what is going on? Or disable this feature for a test? I am writing this on my Dev machine using the browser I test with, so I shall try to paste in tech info below. Just to reiterate, in this browser I can have my test server in one tab, my live server in another tab, test server popup works; live server popup does not. Thanks in Advance, Richard