Support developer edition

Mozilla just [released the new FF Developer edition](https://hacks.mozilla.org/2014/11/mozilla-introduces-the-first-browser-built-for-developers-firefox-developer-edition/) about a month ago.  It's not entirely clear, but it [seems like FF Developer will replace the Aurora channel and naming scheme](http://forums.mozillazine.org/viewtopic.php?p=13857797&sid=4c70ce8d993c52960fe0ef49d194f4de#p13857797).  Either way, it seems wise to add support for Developer Edition.  I've gone ahead and done so.  I don't have access to a Mac at the moment, but I'm 90% sure the path I've popped in for the Developer Edition bin is correct.  Besides that, it seems to work great.