Examine source code of Correios Helper

{
  "manifest_version": 2,
  "name": "Correios Helper",
  "description": "Simples extensão para facilitar o rastreamento de pacotes nos Correios.",
  "version": "0.27",
  "browser_action": {
    "default_icon": "icon128.png",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "js/jquery-3.2.1.min.js",
      "js/history.js",
      "js/tracker.js",
      "js/background-alarm.js"
    ]
  },
  "icons": {
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "permissions": [
    "storage",
    "alarms",
    "http://webservice.correios.com.br/"
  ]
}