Examine source code of Always Smile

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Always Smile",
  "description": "Always use smile.amazon.com when shopping at amazon.com",
  "version": "0.0.0.1",
  "manifest_version": 2,
  "background": {
    "service_worker": "background.js"
  },
  "permissions": [
    "webRequest",
    "*://www.amazon.com/*",
    "webRequestBlocking"
  ],
  "icons": {
    "16": "/images/icon16.png",
    "32": "/images/icon32.png",
    "48": "/images/icon48.png",
    "128": "/images/icon128.png"
  }
}