npm run firefox crashes

[daviddahl]

npm run firefox runs a new copy of firefox 48.0.1 for a bit but then crashes. I am able to connect to the running instance from debugger.html at first

see:
http://pastebin.com/anQcuU4V

[jasonLaster]

Thanks, I think this is because we need to use marionette after 47.

[jasonLaster]

@jacobjzhang, @daviddahl just pushed a fix. It would be great if you could pull and see if this fixes it.