Examine source code of Flappy Bird Html5

{
  "manifest_version": 2,
  "name": "Flappy Bird",
  "version": "1.0",
  "description": "Flappy Bird is one of the most popular fun on the Internet before",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": {
      "128": "images/flappy-bird-logo.png"
    },
    "default_title": "Open Popup",
    "default_popup": "popup.html"
  },
  "icons": {
    "128": "images/flappy-bird-logo.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{e86afa95-6ddf-46d9-ba5c-e45b43901289}"
    }
  }
}