Examine source code of Unread Email Notifier

{
  "manifest_version": 2,
  "name": "Unread Email Notifier",
  "version": "1.0",
  "description": "Display the number of unread emails from all accounts.",
  "permissions": [
    "storage",
    "tabs",
    "*://mail.google.com/*",
    "*://mail.yahoo.com/*",
    "*://outlook.live.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/icon.png"
    }
  },
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8c043459-93e2-47f0-9282-cd026b607878}"
    }
  }
}