Examine source code of Amazon Smile Redirecting

{
  "manifest_version": 2,
  "name": "Amazon Smile Redirecting",
  "icons": {
    "16": "smiley16.png",
    "48": "smiley48.png",
    "128": "smiley.png"
  },
  "description": "Every 'www.amazon.com(de, co.uk)/...' kind of link is redirected to 'smile.amazon.com(de, co.uk)/...'",
  "version": "1.5",
  "permissions": [
    "webRequest",
    "webRequestBlocking",
    "*://www.amazon.com/*",
    "*://www.amazon.co.uk/*",
    "*://www.amazon.de/*"
  ],
  "background": {
    "scripts": [
      "plugin.js"
    ]
  }
}