I'm so confused as to whether Mozilla Thunderbird utilizes ChatZilla itself as the irc backend or if the developers simply re-wrote irc support from the ground

I'm so confused as to whether Mozilla Thunderbird utilizes ChatZilla itself as the irc backend or if the developers simply re-wrote irc support from the ground up... ChatZilla is by far my favorite client and I would love if it could support new IRCv3 features.