Examine source code of Network Status Indicator

{
  "manifest_version": 3,
  "name": "Network Status Indicator",
  "version": "1.0",
  "description": "Shows a green circle when online, and a red circle when offline.",
  "browser_specific_settings": {
    "gecko": {
      "id": "@NetworkStatusIndicator",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      },
      "strict_min_version": "58.0"
    }
  },
  "action": {
    "default_title": "Checking network..."
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ]
}