Examine source code of Simple Calculator

{
  "manifest_version": 3,
  "name": "Simple Calculator",
  "version": "1.0",
  "description": "A simple calculator accessible from the toolbar button.",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Calculator",
    "default_popup": "popup/popup.html"
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "simple-calculator@firefox.com"
    }
  }
}