Examine source code of download-finished-notify

{
  "manifest_version": 2,
  "name": "download-finished-notify",
  "version": "1.1",
  "description": "Creates a notification whenever a download is finished",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "background": {
    "scripts": [
      "download-notify.js"
    ]
  },
  "permissions": [
    "downloads",
    "notifications"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{35cb6e59-9ac8-48e8-b974-d00fcb248301}"
    }
  }
}