Examine source code of Rate Overlay

{
  "manifest_version": 2,
  "name": "Rate Overlay",
  "version": "5.6",
  "description": "See foreign prices in the money you think in. One click annotates the page, another click removes the annotations.",
  "browser_specific_settings": {
    "gecko": {
      "id": "{e131c2c9-822c-4261-b9f6-e1aa56d1eabd}",
      "strict_min_version": "101.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "32": "images/icon-32.png",
    "48": "images/icon-48.png",
    "64": "images/icon-64.png",
    "96": "images/icon-96.png",
    "128": "images/icon-128.png"
  },
  "browser_action": {
    "default_title": "Rate Overlay",
    "default_popup": "scripts/popup.html",
    "default_icon": {
      "32": "images/icon-32.png",
      "48": "images/icon-48.png",
      "64": "images/icon-64.png",
      "96": "images/icon-96.png",
      "128": "images/icon-128.png"
    }
  },
  "permissions": [
    "storage",
    "activeTab",
    "https://open.er-api.com/*",
    "https://api.frankfurter.app/*"
  ]
}