Examine source code of GitHub Tetris Game

{
  "manifest_version": 2,
  "name": "GitHub Tetris Game",
  "version": "0.2.2",
  "description": "Play Tetris on your GitHub contribution graph.",
  "permissions": [
    "activeTab",
    "notifications"
  ],
  "background": {
    "scripts": [
      "extension-activate.js"
    ]
  },
  "browser_action": {
    "default_title": "Play",
    "default_icon": {
      "16": "icon.png",
      "48": "icon.png",
      "128": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a1ac4a53-e297-413d-905d-18b78eb20c5b}"
    }
  }
}