Is this about using Legacy extensions in Firefox that won't be supported in Firefox 57?

• https://addons.mozilla.org/en-US/firefox/search/?tag=firefox57

You should switch to the Firefox 52 ESR release if you do not want to use Firefox 57+ releases.

• https://www.mozilla.org/firefox/organizations/faq/
• https://www.mozilla.org/en-US/firefox/organizations/all/
• https://www.mozilla.org/en-US/firefox/52.4.0/releasenotes/

That way you will still receive security updates until June next year.

Type about:preferences#advanced<enter> in the address bar.

Under Advanced, Select Update. Check the settings.

Also turn off Use a background service to install updates

FredMcD said

Type about:preferences#advanced<enter> in the address bar. Under Advanced, Select Update. Check the settings. Also turn off Use a background service to install updates

Never Check for Updates is what you want. As states Not Recommend as updates fix security issues for your browsing safety.

You have answered why you want to remain at version 56.0.1 Firefox 57 Quantum will be much better/faster/less ram and will have fixed all issues in 56 and https://www.mozilla.org/en-US/firefox/quantum/ and see https://www.theregister.co.uk/2017/09/26/mozillas_new_firefox_quantum/

Most Extension Developers are updating their programs for ver 57 and if not there are/will be alternatives.

Fyi: Please update your Flash to new version released 5 days ago https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, Win IE . . . .) Note: Other software is offered in the download. <Windows Only>

Please let us know if this solved your issue or if need further assistance.

Select Never Check For Updates

Also turn off Use a background service to install updates