Examine source code of XE.com currency button

{
  "manifest_version": 2,
  "name": "XE.com currency exchang rate",
  "version": "1.0",
  "description": "XE.com foreign exchange button",
  "background": {
    "scripts": [
      "button.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{e84bb1bb-b167-4e87-ab1d-f3f2a8c34eae}"
    }
  }
}