This is a great way to partially restore the old, neutral look. In addition, I would recommend setting the following two flags to “false” on the about:config page: browser.nova.enabled and browser.newtabpage.activity-stream.nova.enabled. Enjoy the design you’re used to!

At least the color gets right.

The rounded tabs are an absolute eyesore, and the new circular pinned tabs look downright ridiculous.

Good that this official theme has been provided for people who don't like the gradients that are everywhere in Firefox v157. It's a shame that normal and private windows are no longer discernible at a glance though, that really ought to be tweaked.

And yes I know that I could create my own theme and tweak this myself, but there really should be a functional, non-garish design available out of the box (as was the case previously).

The only okayish theme came with Nova. I hate the radius though.