Examine source code of How big is that?

{
  "manifest_version": 2,
  "name": "How big is that?",
  "version": "1.3",
  "description": "How big is that?",
  "homepage_url": "https://github.com/vantezzen/howbigisthat",
  "icons": {
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png"
  },
  "permissions": [
    "contextMenus",
    "activeTab",
    "storage"
  ],
  "options_ui": {
    "page": "options/index.html",
    "open_in_tab": true
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "web_accessible_resources": [
    "inject.html"
  ]
}