The new Firefox design is really not for me, and Mozilla, instead of focusing on more important issues, is spending time changing something nobody asked for.

A Hacker News comment by n4bz0r shares a rollback setting: open about:config, find browser.nova.enabled, and set it to false.

Let's see how long this option stays available.

Hacker News thread: The new Firefox design is here

Mozilla's original announcement of the new design has more context.