Examine source code of BackPack

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "author": "Filip Rafajec",
  "version": "2.0.0",
  "name": "BackPack",
  "short_name": "Backpack",
  "description": "Your personal pocket alarm for mozilla with notifications.",
  "offline_enabled": true,
  "permissions": [
    "storage",
    "notifications"
  ],
  "icons": {
    "32": "icon-34.png",
    "128": "icon-128.png"
  },
  "browser_action": {
    "default_title": "Alarm manager",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{40c049c7-de7e-45ad-9cc8-d8345f5f8537}"
    }
  }
}