Examine source code of Marble Extension

{
  "manifest_version": 2,
  "name": "Marble Extension",
  "version": "1.0",
  "description": "An extension that adds marbles to each URL with physics properties based on the characters in the URL.",
  "permissions": [
    "activeTab",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "marbles.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{9d1f0a98-b66e-4e52-b495-5a518c520dbe}"
    }
  }
}