Congratulations, now you've got a build set up! Now you can start contributing code.
If you're a new contributor, you can pick a "good first bug" [http://www.joshmatthews.net/bugsahoy/?mobileandroid=1&unowned=1&simple=1 | here], or jump into #mobile to ask.
These [[Mobile/Fennec/Android/CommonTips|common Tips and How-To's]] will help you get started.