First, Type about:preferences#advanced<enter> in the address bar. Under Advanced, Select Update.

[v56+] Type about:preferences#general<enter> in the address bar. Select Update.

Select Never Check For Updates.

Also turn off Use a background service to install updates <Windows Only>

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

I have already that settings applied, it's written in the OP btw so it doesn't work. Firefox still updates itself automatically, at about once a week I open firefox and boom - version 57 installed.

Would you please take a look at the solution here  :

[Link removed by mod] Would that work for you as well  ?

You should not use Firefox 56 anymore. You should be using the latest version of Firefox due to security issues that are known in old versions and are used in automatic hacking tools. What add-ons are you having difficulty with? We may be able to find replacements.

Happy112 said

Would you please take a look at the solution here  : [Link removed by mod] Would that work for you as well  ?

I followed your link and I uninstalled the mainentance service and disabled network access in firewall for updater.exe. Now time will show if it's working. Thanks.

Tyler Downer said

You should not use Firefox 56 anymore. You should be using the latest version of Firefox due to security issues that are known in old versions and are used in automatic hacking tools. What add-ons are you having difficulty with? We may be able to find replacements.

There's no usefull replacements, at least I can nod find any that's working as original addons. It's these: AutoCopy 2 Classic Theme Restorer FlashGot gtranslate Restart Tab Mix Plus

@ Tyler Downer :

In the link that you removed, you apparantly did not notice the following warning, that is posted in that thread numerous times :

"You should not follow any answer that advises you to disable automatic updates: that's bad advice that can open your computer up to being infected with malware."

Fact remains that some users have valid reasons for not wanting to update (right now), and it's better to respect their wishes than to just let them say 'Goodbye' to Firefox.

There is no reason to use Firefox 56. If you have add-ons that have no web extension replacement, you can use Firefox ESR. Using 56 leaves you and the internet at risk for attack

Tyler Downer said

Using 56 leaves you and the internet at risk for attack

You're right - hence the bolded text in the link you removed.

But when I have to choose between letting users leave Firefox and respecting their wishes not to update (for now) : I choose the latter.

Maybe we shouldn't give a link to this article anymore :

https://support.mozilla.org/en-US/kb/install-older-version-of-firefox?cache=no

And maybe Mozilla should remove the option 'Never check for updates' in Preferences .......

Thanks for your replies, I will stick with the ESR version for now. Didn't know that such version exist.