Step one: 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

Step two: Note: Some versions of Quantum change how the data files are set up, so they may not be backward compatible.

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

right now I have 89. uninstall it and any ver firefox you do try to install gets upgraded to this crap 89 where nothing looks correct nor works correctly. And this crap of less secure, this has happened the every update at least. every firefox is insecure. More like they are trying to collect more user data and the attempts are not working, So new ver firefox. And the appearance, I want to see the old look back. Has firefox turned into a bunch of conformists. Why not make it look like all the icon using "programs" out there. An icon of an F and some gibberish under it does not give me anything that relates to the page I was viewing. VERY informative, NOT. I see no purpose in forcing these changes unless there is money to be made. Give the option. It has become most impossible to find a browser that functions reliably. Chrome has no visual functionality. And I absolutely refuse to use any microsoft product I don't have to. Never tried Opera, but it may be next to be tried.

I see that Opera is also a group of conformists. Scrap the icons! PLEASE

After installing old version of firefox, I had to disconnect from internet, open firefox, go to options to change update settings so that it doesn't auto download v89. Close firefox, reconnect internet.

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