Examine source code of GitHub Pages 404

{
  "manifest_version": 2,
  "name": "GitHub Pages 404",
  "version": "1.0.1",
  "description": "Provides links to Owner's Profile and GitHub Repo on a GitHub Pages 404 page",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.github.io/*"
      ],
      "js": [
        "pages404.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{8069eea0-7a92-4f87-9c73-a2795f82d9a7}"
    }
  }
}