Examine source code of Currency Converttter

{
  "manifest_version": 2,
  "name": "Currency Converter",
  "version": "0.6.9",
  "description": "Daily rate currency converter powered by exchangerate-api.com.",
  "browser_action": {
    "default_icon": "icons/icon_128.png",
    "default_title": "Currency Converter",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "scripts/background.js"
    ]
  },
  "icons": {
    "16": "icons/icon_16.png",
    "32": "icons/icon_32.png",
    "48": "icons/icon_48.png",
    "128": "icons/icon_128.png"
  },
  "permissions": [
    "*://open.er-api.com/"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{ba9c03a6-05ae-4def-89a7-d884cb589361}"
    }
  }
}