I run Linux Debian 12 (bookworm), and there seems to be no way to disable Firefox from automatically starting up after system boot. I've searched through settings, read countless articles on the internet, looked at system auto-startup applications, but wasn't able to find anything that worked. I even looked in about:config, but couldn't find anything. Firefox isn't automatically started by my system and there is no parameter that disables it. I also didn't click through any choices about autostart when I first opened Firefox.