Examine source code of Save Selection

{
  "manifest_version": 3,
  "name": "Save Selection",
  "version": "1.0",
  "description": "Saves selected text to extension-local storage.",
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_title": "Save Selection",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "48": "icons/icon.svg"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "ext-save-selection@example.com",
      "data_collection_permissions": {
        "required": [
          "none"
        ],
        "optional": [],
        "description": "This extension does not collect or transmit user data."
      }
    }
  }
}