Examine source code of Link Tab Checker

{
  "manifest_version": 3,
  "name": "Link Tab Checker",
  "version": "1.0",
  "description": "Checks if a link opens in a new tab.",
  "permissions": [
    "activeTab"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon16.png",
      "48": "icon48.png",
      "128": "icon128.png"
    }
  },
  "service_worker": "background.js",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "your-addon-id@example.com"
    }
  }
}