These three prefs are all that is needed.
user_pref("network.proxy.socks_remote_dns", false); user_pref("extensions.torlauncher.start_tor", false); user_pref("network.proxy.type", 0);
The only issue is system-tor is running in the background. Well maybe not an issue but some (most?) users would expect Tor to be completely disabled. This should be mentioned in the documentation