Examine source code of Article Length Estimator

{
  "manifest_version": 2,
  "name": "Article Length Estimator",
  "version": "1.0",
  "description": "Estimate the time needed to read an article based on word count.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{d7531fd9-6d18-4818-8286-89cdf06b236d}"
    }
  }
}