Examine source code of Gentle-Start

{
  "manifest_version": 2,
  "name": "Gentle-Start",
  "version": "1.0.0",
  "description": "Fade in any audio/video on a page (0.3–1.0s) to avoid sudden loud sounds.",
  "permissions": [
    "storage",
    "activeTab",
    "tabs"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_action": {
    "default_title": "Gentle-Start",
    "default_popup": "popup.html"
  },
  "icons": {
    "48": "icons/icon48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "gentlestart-39041b409a92@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}