userAgent protection causes "TypeError: this.editor is null" on some versions of dojo.js

[rolandog]

Describe the bug

Somehow, the userAgent protection is breaking a site (inability to scroll) that uses dojo.js (Dojo Toolkit).

The console shows two "TypeError: this.editor is null" errors.

To Reproduce
Steps to reproduce the behavior:

1. Ensure User-Agent Randomiser protection is ON by default (In my case, I'm using Linux/Firefox for the settings)
2. Go to a (private) course in KleurRijker (this will be hard to reproduce, as you need to have purchased a book with an access code)
3. Try to scoll (with no success)
4. See errors in console TypeError: this.editor is null

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 21.04
• Browser: Firefox 93.0b8
• Version: 3.0.7

Additional context
Dojo version on that website:

dojo.version.toString()
"1.14.8 (9736f469)"

The userAgent strings don't really change much:

With userAgent protection:

navigator.userAgent
"Mozilla/5.0 (X11; Linux x86_64) Gecko/20100101 Firefox/89.0"

Without userAgent protection:

navigator.userAgent
"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:93.0) Gecko/20100101 Firefox/93.0"