Examine source code of GitHub Theme Customizer

{
  "manifest_version": 2,
  "name": "GitHub Theme Customizer",
  "version": "1.0",
  "description": "Customize GitHub theme to your liking.",
  "permissions": [
    "scripting",
    "storage"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://github.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{3c6ad1a2-a699-4116-97f4-3d4b28930673}"
    }
  }
}