Examine source code of AlwaysSmile

{
  "manifest_version": 2,
  "name": "AlwaysSmile",
  "version": "1.3.2",
  "description": "Redirects Amazon.com to smile.amazon.com.  This helps you always donate part of your purchase by purchasing at smile.amazon.com!",
  "icons": {
    "16": "icon-16.png",
    "32": "icon-32.png",
    "48": "icon-48.png",
    "128": "icon-128.png"
  },
  "background": {
    "scripts": [
      "smile.js"
    ]
  },
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "https://www.amazon.co.uk/*",
    "https://www.amazon.com/*",
    "https://www.amazon.de/*"
  ]
}