There are three ways to get in communication with the Bugzilla developers: IRC, Bugzilla, and the Developers Mailing List.
The best way to contact the Bugzilla developers is through IRC.
Most of us are in #bugzilla on irc.mozilla.org. We all live in different time zones, though, so different developers are awake at different times. The channel may be a bit dead if it's currently night time in the United States and not yet morning in Europe, though usually somebody is there.
If you can't easily get on IRC, you can use the Bugzilla IRC Gateway. That way you don't have to install anything!
If you want to become a core Bugzilla developer, the absolute best way is just to hang out in IRC for a long time. If you make it plain that you're a programmer and you want to work on Bugzilla, eventually somebody will just grab you and say, "Work on this!" Do be patient, though--that doesn't happen instantly.
What If Nobody Answers Me on IRC?
If you come into IRC to ask a question, and nobody answers, just wait a while, or come in again at a different time! We're not ignoring you, we're just not there! We always answer people's questions, when we're around.
If you have a question about a particular bug, or some feedback on it, the best thing to do is to comment on that bug itself. We use bugzilla.mozilla.org for tracking Bugzilla development.
However, if nobody answers your question for a long time (after several days), come into IRC and ask.
If you want to make a broad announcement to all Bugzilla developers, you should use the developers mailing list. Bugzilla developers call this mailing list "developers@" for short.
If you're going to be a Bugzilla developer, you should definitely be on this list. It isn't a high-volume list, although once in a while we do have long discussions on the list.
However, if you just have a simple question to ask, don't use the list, use IRC.