Sorry Dmitry this add on is only partially working on latest Firefox 64 bit version for Youtube. It works on the short videos.
In the comments and replies it is not working at all. Also on the main video title Like/Dislike it still only shows the likes. Interestingly now it also shows "Disabled by Owner" which I never saw before the add-on. Hopefully you can resolve it.

Update: The Dislikes are now visible on the Main YT videos - Thanks.

Is there any way to see the Dislikes in the Comments section of the Video ?

EN-US: Something that should have been there without the need for any extension/addon, but YouTube made this misguided and anti-consumer move to remove something that is basic in today's world. Let's face it, they only removed it because of the extremely negative reviews on YouTube's official retrospective videos. Anyway, in light of this, an essential and highly welcomed extension to enhance the usability and convenience of YouTube itself and how people are reacting to other videos on this platform.

PT-BR: Algo que já deveria ter sem qualquer uso de extensão, mas que o Youtube deu esse movimento errado e tão anti-consumidor de tirar algo que é básico nos dias de hoje, que convenhamos só tiraram por causa das avaliações extremamente negativas nos vídeos oficiais do Youtube, mas enfim, diante disso, uma extensão essencial e extremamente bem-vinda para melhorar a utilização e praticidade do próprio Youtube e como as pessoas estão reagindo aos demais vídeos dessa plataforma.

As a content creator myself, this is extremely inaccurate, probably does more harm than good, you need to update this asap, by allowing content creator themselves to show the REAL DISLIKE amount from youtube studio. On average this reports twice as many dislikes than actual dislikes, NOT GOOD.

Majority of Youtube Audience do not create content themselves, or do it enough to know this and will be deceived by this unintentional mistake you are making, please FIX IT.

Stopped working since YouTube updated its design a few weeks ago.

Лучшее расширение! Работает безотказно и с последними обновлениями счётчи кдизлайков отображается как надо

Works perfectly for returning that dislike counter, and with the new added customization options make it even better!

Works perfect on desktop. Any plans on adding support for youtube on mobile browser as well? (m.youtube.com)

we needed this thank you

la tuve que desintalar por que me bloqueaba youtube y youtube music