2022: Please try again!! :) (We found a great solution and there is no alternative)
2021: Hi, this feature was fixed / completed in our new version at https://github.com/code4charity/YouTube-Extension. Our Firefox version started recently. Yet we look forward to update the Firefox version soon and often.
I understand 'reverse playlist' is a legendary feature as people miss it. (Because other projects, providing this feature only, resigned, despite they had many users. Because youtube changed this repeatedly.) Thus we temporarily removed the feature from our descriptions.
Yet that is not what you can possibly rate here. What you are rating can only be our whole work with 100 features and an insane amount of work. That's how we always called and describe. Yet your rating actually has a (negative) impact