Examine source code of Codeforces++

{
  "name" : "Codeforces++",
  "description" : "Codeforces extension pack",
  "version" : "2.1.3",
  "manifest_version" : 2 ,
  "permissions" : [
    "storage" ,
    "tabs //" ,
    "*://codeforces.com/*" ,
    "http://fonts.googleapis.com/*" ,
    "https://fonts.googleapis.com/*" 
  ],
  "content_scripts" : [
    {
      "matches" : [
        "*://codeforces.com/*" 
      ],
      "js" : [
        "browser-polyfill.min.js" ,
        "contentScript.js" 
      ],
      "css" : [
        "common.css" 
      ],
      "run_at" : "document_start" 
    }
  ],
  "web_accessible_resources" : [
    "*.js"
  ],
  "background" : {
    "persistent" : false ,
    "scripts" : [
      "browser-polyfill.min.js" ,
      "background.js" 
    ]
  },
  "browser_action" : {
    "default_popup" : "popup.html",
    "default_title" : "Codeforces++"
  },
  "icons" : {
    "16" : "icons/16x16.png",
    "32" : "icons/32x32.png",
    "48" : "icons/48x48.png",
    "128" : "icons/128x128.png"
  }
}