Writing patches mainly for SpiderMonkey / Updating documentation / Developing some Add-ons
Impressive contributions to the JS Engine and XPConnect - see bug https://bugzilla.mozilla.org/show_bug.cgi?id=1079919#c21
arai is very helpful on IRC and assists newcomers getting started with contributions. Furthermore, arai also reports and fixes bugs.
Intense MDN documentation: https://developer.mozilla.org/en-US/dashboards/revisions?user=Noitidart Expert on js-ctypes and especialy mac os obejctive c, he added the documentation on MDN for it He even helps extensively with solving other peoples issues: http://www.unmht.org/forum/en/4774.html (this is exmaple of objc jsctypes help)