Examine source code of Subscriber

{
  "name": "Subscriber",
  "description": "Subscription extension for youtube and twitch",
  "version": "0.2.1.0",
  "manifest_version": 2,
  "icons": {
    "48": "res/48.png",
    "96": "res/96.png"
  },
  "browser_action": {
    "default_popup": "menu/menu.html"
  },
  "background": {
    "page": "background/bg.html",
    "persistent": true
  },
  "content_scripts": [],
  "permissions": [
    "tabs",
    "activeTab",
    "storage",
    "https://www.youtube.com/*",
    "https://www.twitch.tv/*",
    "https://twitchrss.appspot.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "piikulii@yandex.ru"
    }
  }
}