copy the install addon script:
  file.managed:
    - name: {{ salt['user.info']( pillar['username'] ).home }}/bin/install_firefox_addon
    - source: salt://files/install_firefox_addon
    - user: {{ pillar['username'] }}
    - group: users
    - mode: "0755"

{% for name, args in pillar['firefox']['addons'].items() %}
Downloading {{ name }} Firefox xpi:
  cmd.run:
    - name: {{ salt['user.info']( pillar['username'] ).home }}/bin/install_firefox_addon {{ args['name'] }} {{ args['url'] }}
    - unless: grep -oP '(?<=\},\"name\":\"){{ name }}' {{ salt['user.info']( pillar['username'] ).home }}/.mozilla/firefox/*.default*/addons.json
    - user: {{ pillar['username'] }}
{% endfor %}