"As I said, for the past few updates, I have not approved it but said "ask me later". After a few t

"As I said, for the past few updates, I have not approved it but said "ask me later". After a few times of doing that, over a week or two probably, it downloads on its own, without my approval."

If you happen to miss the dialog window that gives you the option to "Ask me later" as a method of postponing the inevitable, that dialog will time out in like 15 seconds and then go ahead & download the update without waiting for your response. That has always been the action of that preference since Mozilla started automatic updates on Firefox - like 7 to 8 years ago. Never check for updates (not recommended : security risk) does still allow the user to postpone updating Firefox - but not forever.

Mozilla feels very strongly that their users run the latest and most secure browser which is available. Mozilla would rather that people use a different currently up-to-date browser, than continue to use an outdated version of Firefox.