I've flipped to notify the setting in "about:preferences" to the other available one "Check for updates but let you choose to install them", but it automatically flips back to autoupdate after a while - I've had firefox updating on its own a few times because of that sometimes really messing up my extensions and settings. I prefer having control of my own, backing up the portable version myself and manual updates. I've also flipped to false these flags in "about:config": app.update.auto app.update.auto.migrated app.update.enabled but they aren't doing anything.