[Update 2014-01-16: A point of clarification. There are two possible ways to send a password for IRC. One is supported in the Instantbird UI – it’s the one that automatically identifies your nick with NickServ, the bot which makes sure people don’t steal other people’s nicks. The other, which is rarer but which I needed, involves sending a password to connect at all, using the PASS command in the IRC protocol. That is what is documented here.]
I was trying to do this; turns out it currently requires about:config manipulation and is not documented anywhere I can find.
Using about:config (type /about config in a message window, or access via Preferences), set the following prefs:
to the obvious values. Other useful tip: if the IRC server uses a self-signed cert, connect to it on the right port using Firefox and HTTPS, and you can save the cert out of the warning/exception dialog you get. You can then import it into Instantbird using the deeply-buried Certificate section of the Advanced Preferences and it will trust the cert and connect. (I think this is what I did, although memory is hazy.)
Thanks for posting this, Instantbird will give a warning in the account manager if you connect to a server with a self signed certificate and prompt you to add it. (This was fixed for Thunderbird 17 in https://bugzilla.mozilla.org/show_bug.cgi?id=780749 and Instantbird 1.4 in https://bugzilla.mozilla.org/show_bug.cgi?id=954534.) The link can be a little hard to see on Windows due to the highlighting color: https://bugzilla.mozilla.org/attachment.cgi?id=8353991
I’ve come across very no servers “in the wild” that require an actual server password and username…except ZNC or other bouncers, which we’ve made a specific effort (although some of these improvements are waiting on Instantbird 1.6 to be released). We’ve (somewhat) optimized the UI for the novice IRC user (i.e. it’s confusing that IRC uses *two* passwords, and a nick and a username); so that someone new to IRC can connect ASAP without answering tons of questions. There is an open bug about exposing this in the UI (https://bugzilla.mozilla.org/show_bug.cgi?id=1016494), if you have further suggestions I’d love to hear them! (Also, that bug has the same workaround that you posted above. :))