An easy way to get started is "Bugs Ahoy", a Bugzilla search engine that lets you search by programming language and feature area among bugs tagged as "good first bug" with a Mozilla mentor's contact info:
Again, thanks for this. I've intended to get involved but never got around to figuring out how. Having this run across my screen motivated me to get a nick registered, and say hello in the channel.
http://www.joshmatthews.net/bugsahoy/?unowned=1