Examine source code of AmazonTrackLink

{
  "manifest_version": 2,
  "name": "AmazonTrackLink",
  "version": "1.1",
  "description": "Creates a link on shipment status page (only Germany)",
  "icons": {
    "48": "icons/trackit-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.amazon.de/gp/your-account/ship-track/*"
      ],
      "js": [
        "linktrack.js"
      ]
    }
  ]
}