It's simple and one-click for Firefox and Chrome
If you use Chrome (or alternative web browsers that use Chromium as web engine such as Vivaldi), the extension is available at the CWS (Chrome Web Store). If you use Firefox, click here to install the exension.
Scrobbly will ask you to login to AniList and/or Kitsu.
You don't understand something? Contact me with Telegram or drop me an e-mail.