Examine source code of Notification Silence

{
  "manifest_version": 2,
  "name": "Notification Silence",
  "version": "1.0",
  "description": "Blocks all browser notifications on websites.",
  "icons": {
    "64": "icons/icon64.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{025a0b4a-b1e7-4484-9f8a-2ebe7be79a87}",
      "strict_min_version": "114.0"
    }
  }
}