Examine source code of Messenger Notifications

{
  "manifest_version": 3,
  "name": "Messenger Notifications",
  "version": "1.0.1",
  "description": "Get desktop notifications when you receive new Facebook Messenger messages",
  "permissions": [
    "notifications",
    "storage",
    "tabs"
  ],
  "background": {
    "service_worker": "background.js"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.facebook.com/messages/*",
        "https://www.facebook.com/messages",
        "https://www.messenger.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    },
    "default_title": "Messenger Notifications"
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "update_url": "https://edge.microsoft.com/extensionwebstorebase/v1/crx"
}