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 ?