16-10-2023 working solution:

There has been an update for the extension which requires you to install it manually for now:

- remove the original add-on from Firefox
- download firefox.zip from https://github.com/Anarios/return-youtube-dislike/releases/tag/v3.0.0.11
- go to about:addons
- Under the cogwheel - click on 'Debug Add-ons'
- click on Load Temporary Add-on...
- select firefox.zip

I recommend to check reddit r/youtube where I found this solution.