firefoxPref can't change javascript.enabled


I have tried to measure a performance of a website without JS. I don’t want just block js requests, but simulate that JS is disabled in the browser.
So I gave a try to - the setting itself seems to be working fine (e.g. firefoxPref general.useragent.override “TEST” is ok).
But I do not see any difference between javascript.enabled ( true or false:

firefoxPref javascript.enabled true navigate

firefoxPref javascript.enabled false navigate

Two questions:

  1. Is there anything specific about javascript.enabled? Is this an expected behavior?
  2. Any recommendation how to simulate javascript disabled?

Ok, there is an easier - trivial way - to disable JS. Trying to solve my issue I found and this piece of code if (_test._noscript) { user_prefs += "user_pref(\"javascript.enabled\", false);\r\n"; }
led me to Advanced Settings > Advanced > Disable Javascript checkbox on