Examine source code of Privacy Window

{
  "manifest_version": 2,
  "name": "Privacy Window",
  "version": "1.3.1",
  "description": "Dim the tab except for a window around the mouse.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_title": "Toggle Privacy Window"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "privacy-window@yourname",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}