Examine source code of eBay UK Basket button

{
  "manifest_version": 2,
  "name": "eBay UK Basket",
  "version": "1.2",
  "description": "eBay UK Basket opens in a tab",
  "background": {
    "scripts": [
      "button.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{91cf9285-980e-46fe-b6dd-eb9f744c2bd6}"
    }
  }
}