Examine source code of eBay UK button

{
  "manifest_version": 2,
  "name": "eBay UK button",
  "version": "1.0",
  "description": "eBay UK opens in a tab",
  "background": {
    "scripts": [
      "button.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{ba62418b-3a36-4cb8-b320-46f373335ddd}"
    }
  }
}