• https://www.mozilla.org/ru/firefox/download/thanks/

• A user.js file is an alternative method of modifying preferences
• How to Change Firefox Proxy Settings Programmatically?
• Переменные окружения
• Автоматизация использования SQUID

server# FIREFOX_USER=user2

debian# FIREFOX_PROFILE_FOLDER=/home/${FIREFOX_USER}/.mozilla/firefox/$(grep 'Path.*esr' /home/${FIREFOX_USER}/.mozilla/firefox/profiles.ini | cut -d'=' -f2)
alt# FIREFOX_PROFILE_FOLDER=/home/${FIREFOX_USER}/.mozilla/firefox/$(grep 'Path.*default-default' /home/${FIREFOX_USER}/.mozilla/firefox/profiles.ini | cut -d'=' -f2)

server# cat ${FIREFOX_PROFILE_FOLDER}/user.js

user_pref("network.proxy.http", "gate");
user_pref("network.proxy.http_port", 3128);
user_pref("network.proxy.ssl", "gate");
user_pref("network.proxy.ssl_port", 3128);
user_pref("network.proxy.no_proxies_on", "localhost,127.0.0.1,isp.un,corpX.un");
user_pref("network.proxy.type", 1);

chown ${FIREFOX_USER}:${FIREFOX_USER} ${FIREFOX_PROFILE_FOLDER}/user.js

Помогает:

about:config

network.auth.use-sspi;false