For people looking for a project, Mozilla has a lot of documentation and tools to help first-time contributors. "Contributing to the Mozilla Codebase" [1] documents how to get the code and build your own Firefox. "Bugs Ahoy" [2] is a Bugzilla search engine that filters "good first bugs" based on programming language and interests.
[1] https://developer.mozilla.org/en-US/docs/Introduction
[2] http://www.joshmatthews.net/bugsahoy/