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> --------------- [https://support.mozilla.org/en-US/kb/install-older-version-of-firefox?cache=no 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 [https://www.mozilla.org/en-US/firefox/organizations/ Firefox; Extended Support Release] {web link} [https://www.mozilla.org/en-US/firefox/organizations/notes/ ESR Notes] [https://www.mozilla.org/en-US/firefox/organizations/system-requirements/ System Requirements]