about:config

    app.update.auto → false
    app.update.enabled → false
    app.update.silent → false
    app.update.staging.enabled → false
    extensions.update.enabled → false

sudo mkdir -p /Library/Application\ Support/Mozilla/distribution 
sudo vi /Library/Application\ Support/Mozilla/distribution/policies.json 

{
  "policies": {
    "DisableAppUpdate": true,
    "OfferToSaveLogins": false,
    "OverrideFirstRunPage": "",
    "OverridePostUpdatePage": ""
  }
}


mv /Applications/Firefox.app/Contents/MacOS/updater.app /Applications/Firefox.app/Contents/MacOS/updater.app.bak

/etc/hosts:
127.0.0.1 aus5.mozilla.org
127.0.0.1 download.mozilla.org
127.0.0.1 aus4.mozilla.org  
127.0.0.1 aus6.mozilla.org  
127.0.0.1 push.services.mozilla.com