Examine source code of Offline Preview Mode

{
  "manifest_version": 3,
  "name": "__MSG_extensionName__",
  "version": "1.0",
  "description": "__MSG_extensionDescription__",
  "permissions": [
    "storage",
    "scripting",
    "activeTab",
    "downloads"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": "icon-128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "128": "icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{21c64256-58e2-5e6e-59c0-3fe3b6df8300}"
    }
  }
}