How are bugs prioritized?

kfr- <[email protected]> Fri, 24 Oct 2014 18:55:12 -0700 (PDT)
Newsgroups gmane.comp.mozilla.devel.calendar
Message-ID <[email protected]>
I have a lightning bug that I need fixed. I don't have the skills to fix it myself. The bug was reported by someone else on 2013-05-24. I'm willing to test the fix.

I'm wondering how bugs are prioritized.