Impossible-to-disable background auto-update randomly causes loss of data

[anymouse]

Firefox from Ubuntu 20.04 repository. Version after update is: 85.0.1+build1-0ubuntu0.20.04.1
I am fairly certain that before this update, I was on the latest version available.

Problem description:

Whenever an update is automatically installed in the background, a restart is required. The auto-updates occur in background at seemingly random times, and are, AFAIK impossible to disable (workaround seems to be to install Firefox from different source).
The user always learns about the update only after it has happened already, and it is impossible to open new tabs. Before the restart, strange behavior often occurs, such as inexplicable tab crashes, pages not loading and staying blank, or new tabs being blank or crashing instead of showing the restart prompt. Sometimes, the restart prompt only appears after minutes of fighting with the previously described problems.

This is alarming and frustrating on its own, but in the following cases this leads to loss of data (I have experienced all of them more than once):

-When any content is open in private window, that the user wishes to continue working on. (Because private windows don't get restored after restart)
-When a download is running which is impossible to resume, is from a one-time-download link, or when download is running in a private window.
-When user is working on any work that requires opening a new window to finish, but progress will be lost when browser is closed.
-When a browser with any unfinished work just crashes randomly, most often after following a link or submitting a form.

Steps to reproduce:
1) Install the older version of Firefox from the Ubuntu 20.04 repository (it is likely that this hasn't been fixed in current one either).
2) Start to do any work filling forms, and requiring long downloads and opning new tabs, open few tabs in private window.
3) Wait for it to automatically install an update in background.
4) Wait until restart is prompted or stuff breaks randomly.
5) Restart
6) Your download is failed now, your unsubmitted forms are empty and your private windows are lost.

Things that need to be fixed (in order from most severe):

-Automatic installation of an update should never happen unprompted, while the user is working, and without their knowledge (unless this no longer leads to loss of data). With things like they are now, the absolute minimum is for the updates to happen at start-up, before the user is allowed to do any work.
-User should be allowed to refuse an automatic update if it happens in a way that can lead to loss of data.
User should be able to disable automatic updates.