Examine source code of WikiRank

{
  "manifest_version": 2,
  "name": "WikiRank",
  "version": "1.0",
  "description": "Assessing quality and popularity of the Wikipedia article from current window tab",
  "icons": {
    "48": "icons/wikirank-48.png",
    "96": "icons/wikirank-96.png"
  },
  "browser_action": {
    "default_icon": {
      "19": "button/wikirank-19.png",
      "38": "button/wikirank-38.png"
    },
    "default_title": "WikiRank assessment"
  },
  "background": {
    "scripts": [
      "wikirank.js"
    ]
  },
  "permissions": [
    "tabs"
  ]
}