The most efficient and most effective way, the most simple way, which ensures Firefox won't update even if Firefox somehow bypassed the registry and policy file, is to delete all files with update in its name, so Firefox would never be able to update, this method will be effective to prevent all versions of Firefox from updating.

(You can also turn any system updates off completely in that window, but I don't recommend that.) Myself I prefer the first one thus updates will never install unexpectedly, you will always have to manually trigger the update download and installation process. You probably have the last one selected - select any of the two others. There are three options: only notify about updates, automatically download (but not install) and automatically download & install. You will be able to select what your system should do with security updates (as Firefox updates are classified in that category). In the new window that appears, click again Updates tab. In your System Settings app, go to the last tab (Information) and click Updates at the bottom of that window. The Ubuntu version of Firefox has Firefox's own update mechanism removed, and Firefox is updated by generic system update tool together with all other installed packages if they need an update (that's what you'd expect from a decent package management system, wouldn't you?). I always had - and still have - to manually trigger any updates. I'm using Ubuntu (various releases) for over 10 years, and Firefox never updated automatically in background, not speaking about forced restart.

Updating firefox for windows 10