by Chromium-based browser Vivaldi released v5.6, becoming the first desktop browser to integrate an instance of Mastodon. Users can access the Mastodon instance Vivaldi Social in the browser sidebar. Mastodon is a decentralized alternative to Twitter. Other new features in Vivaldi 5.6 include: fixed tab groups, a redesigned settings page, an optional new privacy-focused search engine, You.com, available to users in the four Anglo-American countries, and more.
https://vivaldi.com/blog/vivaldi-5-6-on-desktop/
