How do you completely turn off update checks in Firefox v64? You can use a policies.json file to disable updates for all users. https://github.com/mozilla/policy-templates/blob/master/README.md or https://winaero.com/blog/disable-updates-firefox-63-above/

You can use a policies.json file in the distribution folder in the Firefox installation folder instead as also listed in the article, so no need to use GPO keys in the Windows Registry. • https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson

Any order I should install versions in? Or don't parallel installs work anymore?

Whatever program is installed last would end up being the default. If you were to try using the computers 'default' controller to do the selecting, it might now show the Firefox icons with versions or location.

If you want to install more than one Firefox browser, each must be installed in its own program folder. Also, each must use its own profile folder.

You can use sync to share data between the profiles. But, some data may not be compatible between different versions of the browsers. Passwords, bookmarks, and history are compatible.

Thank you @FredMcD for your quick response! Apologies for checking back just now, work and life demand priority instead of tinkering with broken updates until I have time to "fix" it and give your helpful tips a try.

...that's the problem with these impositions of all software companies today, they derail perfectly fine user experiences. Sadly even the formerly good ones re-do what we all were used to for many years.

It's as if the CONSTRUCTION company that built YOUR HOUSE comes in (regardless whether you're in or not btw.) and begins "updating" YOUR home. THEY change the colour of your walls, rip out the kitchen and bathroom and replace them with designs and appliances you were not asked about. THEY tear down your curtains and put new ones up (most likely in your least favourite colour), and replace the windows and doors with "safer and better" ones, whether you like their new look and usability or not. If you're (un)lucky, THEY even remove walls and partially, or if you're very lucky completely re-build YOUR house with a "new and improved" layout, more or less space and different room count.

All this rubbish is of course the "most user friendly", "safest" and "best experience" there is and ever was and you just HAVE TO ACCEPT YOUR home being invaded and remodeled without your input or approval. It's for your own good because THEY know best how to keep you safe from burglars, solicitors, squatters and even from yourself. So, stop using what you're used to, like and use what THEY deem best for you. Well, you signed the small print in your purchase contract, nay licensing agreement anyways ... so, say "thank you and please can I have some more"...

I say : GTFO! MY computer, MY PROPERTY, MY decision !

Sorry for the rant, but it's infuriating with these constant updates (interruptions,disimprovement and breakage) from OS and drivers to work tools, to basic utilities like a browser, all the way to games and entertainment software. They all require me to focus my attention on fixing or re-learning if something is broken or "improved".

Glad to help. Safe Surfing.

I understand your frustration. I didnot like where Quantum was going and I am still using v54. So far no real problems.