Great addon! Rated 5 out of 5 stars
Work as intended. Easy to setup. Suggestions:
1) Can setup rules to auto-bypass authentications by rules, or by domain pattern (ex. domains with 1 word only, or internal ip addresses)
2) Can export / import domain list
Some rules may already work
Since I don't do the actual authentication, I can't support any more "rules" than Firefox already supports (https://developer.mozilla.org/en/Integrated_Authentication). However, Firefox does support entering just a domain ("somedomain.com") and anything in that domain will get pass-through auth. You can try putting in an IP address, but if it doesn't work... there's nothing I can do to fix it.
Import/export the list is a great idea. I'll file an issue on http://code.google.com/p/firefox-ntlmauth/issues/list for it.