Examine source code of Bitcoin balance viewer

{
  "description": "Checks balance of wallet addresses",
  "manifest_version": 2,
  "name": "Bitcoin balance viewer",
  "version": "1.1",
  "icons": {
    "48": "icons/icon.png"
  },
  "permissions": [
    "<all_urls>"
  ],
  "browser_action": {
    "default_icon": "icons/icon.png",
    "default_title": "Balance viewer",
    "default_popup": "popup/bal.html"
  }
}