Support Debug Mode from CFX.  Fix #5

debug:  opens debug tab
prefs:
  +x : simple-prefs.x
  y  : preferencesservice.set('y')

Usage:

  cfx run --static-args '{"debug":true, "prefs": {"+username": "Debug
McCode","general.warnOnAboutConfig":false}}'

Conflicts:
	lib/main.js
Merge branch 'master' of https://github.com/mozilla/hotdish

Conflicts:
	lib/main.js