NTLMv1 is known to be insecure but if you need it new setting was introduced:
network.negotiate-auth.allow-insecure-ntlm-v1 - defaults to false and NTLMv1 auth request is silently ignored when sent over HTTP. Set it to true to force NTLMv1authentication prompt.
Disclaimer: NTLMv1 over HTTP is considered insecure - you should know what are you doing
