Examine source code of Window Resize Simple

{
  "manifest_version": 2,
  "name": "Window Resize",
  "version": "1.0.0",
  "description": "Tiny Popup to change width and height for the either browser or viewport",
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "browser_action": {
    "default_title": "Resize Window",
    "default_popup": "popup.html"
  },
  "applications": {
    "gecko": {
      "id": "window-resizer@guegel.eu"
    }
  }
}