There was a previous way by going through the Options menu to disable updates but after disabling it

There was a previous way by going through the Options menu to disable updates but after disabling it through there, when you would go to Help > About Firefox, it would update regardless of that setting.

You can set these prefs in about:config to disable automatic updating:
app.update.auto - false
app.update.enabled - false
app.update.silent - false