Bug Report: Firefox Dark Reader extension causes incorrect firefox version detection

[dominicmason555]

Summary

When the firefox dark reader extension is enabled, while the version of firefox shown in the user agent is correct, however the site incorrectly detects that it is not a recent enough version. Once the extension is disabled for the page, it loads without issue.
The firefox extension is
https://github.com/darkreader/darkreader
https://addons.mozilla.org/en-US/firefox/addon/darkreader/

The bug doesn't prevent users from accessing the site entirely, however it appears to if the user doesn't think to check their extensions and it does not seem obvious that it may be the extension that causes it.

Page

CyberChef encountered an error while loading.

The following browser versions are supported:

Google Chrome 40+
Mozilla Firefox 35+
Microsoft Edge 14+

Your user agent is:
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0

Error Message

SecurityError: The operation is insecure.
Filename: https://gchq.github.io/CyberChef/main.js
Line: 113
Error: SecurityError: The operation is insecure.
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0
CyberChef version: 8.16.0