Examine source code of Focus & Visibility Guard

{
  "manifest_version": 2,
  "name": "Focus & Visibility Guard",
  "version": "1.2.0",
  "description": "Prevents websites from detecting tab switching, window blur/focus, or visibility changes.",
  "icons": {
    "48": "icon.svg"
  },
  "permissions": [
    "<all_urls>",
    "storage",
    "activeTab"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "web_accessible_resources": [
    "page-guard.js"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.svg",
    "default_title": "Focus & Visibility Guard"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "focus-visibility-guard@local.extension",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}