It's there with a long press. I missed it too at first.

https://addons.mozilla.org/en-US/firefox/addon/make-firefox-kittens-again/

That's the one. May your day be brighter with more kittens while doomscrolling the news.

I had a similar one but for the former president. I still have it installed and it always confuses me for a second until I remember it.