I confirm this addon works in Firefox for Android 68.11, Android 12. But this add-on is not in the very limited add-on list of Firefox for Android, So it must first be downloaded using computer ("request desktop site" may work also), open the downloaded xpi file with Firefox for Android 68.11, then select "allow" in popup dialogue. No convoluted process of nightly version needed. Version 68.11 seems the last that could install add-ons and set about:config, so do not update!