Examine source code of Rank Checker

{
  "description": "Změřte si Ranky vašich stránek",
  "manifest_version": 2,
  "name": "Rank Checker",
  "version": "2.2",
  "homepage_url": "https://pagerank.jklir.net/rankchecker.html",
  "icons": {
    "128": "icons/rankchecker_128x128.png"
  },
  "background": {
    "scripts": [
      "rankchecker.js"
    ]
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/rankchecker_16x16.png",
    "default_title": "Změřte Ranky této stránky"
  }
}