It has been updated, after a long period with no updates; it's now finally at the same version as the Google Chrome version.
It provides a lot of great features, which make interacting with Youtube a lot less addicting, frustrating and annoying. Besides allowing you to set limits on Youtube watch it includes toggles for hiding or changing most of the parts of Youtube — which are the parts I find the most useful. It seems to be working without issues, which is great to see.
It's great, I love it, and I'm so glad it's back.

Just because of the "Remove shorts" feature is worth 5 stars

now i can hide those ****ing shorts! thank you, dear developer, thank you so much!

Fantastic extension. I really love it and it's my favorite extension, I just wish it was updated because it's no longer fully working

EDIT:
firefox version was outdated

Thank you for addon works fine...

This thing is great

Nice bro thx

Just fucking great

Beautiful. It just works. Distractions eliminated. Humanity restored.

Lovely extension that helps you manage the appearance of youtube to your exact liking

So many options to customize your YouTube experience. I wish I'd found this long ago.

How about going more untrappy and remove ability to turn extension off for some periods of time?

Super comprehensive Youtube customization tool. I appreciate how many options you have here to make it exactly the way you want it. I downloaded this because I wanted an extension that not only let you get rid of extraneous sidebars, autoplays, etc., which other extensions also do, but I also wanted to get rid of thumbnails which often act as spoilers for content such as sports. Love it!