I was looking at how to use auto-configure on Ubuntu, but I didn't find any good guide, so here's a how to customize Firefox using AutoConfig on Ubuntu or other Linux.
Commands:
sudo add-apt-repository ppa:mozillateam/ppa
snap remove firefox -y
apt update && apt install firefox-esr -y
edit /usr/lib/firefox-esr/defaults/pref/autoconfig.js
//
pref("general.config.filename", "firefox.cfg");
pref("general.config.obscure_value", 0);
edit /usr/lib/firefox-esr/firefox.cfg
//
lockPref("signon.rememberSignons", false);