Examine source code of Email Notifier

{
  "manifest_version": 2,
  "name": "Email Notifier",
  "version": "1.0",
  "description": "Notify when new emails arrive.",
  "permissions": [
    "storage",
    "notifications",
    "https://api.emailservice.com/"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Email Notifier"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6ae4f408-cb35-4a55-962c-3109cefab669}"
    }
  }
}