https://www.bleepingcomputer.com/news/software/new-vivaldi-version-integrates-mastodon-into-the-browser-sidebar/

Vivaldi 5.6 was released today with a Mastodon client integrated directly into the browser's sidebar, seamlessly incorporating the rising social media platform in the browser's interface.

Vivaldi is a cross-platform web browser created by the former co-founder and CEO of Opera Software, Jon Stephenson von Tetzchner.