Examine source code of Flappy Square

{
  "manifest_version": 2,
  "name": "Flappy Square",
  "description": "A ripoff of Flappy Bird for Firefox",
  "version": "1.2.1resigned1",
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html"
  },
  "sandbox": {
    "pages": [
      "test_for_flappy.html"
    ]
  },
  "content_security_policy": "script-src 'unsafe-inline' 'self' 'nonce-abcdefg'",
  "browser_specific_settings": {
    "gecko": {
      "id": "{3b9d531a-1f7b-4866-b6a8-33100da83151}"
    }
  }
}