Exactly what I was looking for! Two most important features of this addon is that is uses a sidebar and it automatically detects feeds on webpages.

It would be nice if dark theme is added.

Very cool! Though dark theme is missing. Any dark theme please?

Dead simple, functional, and seamless integration into older FF versions. Exactly what I was looking for, and I suspect I'll be using this for my RSS needs from now on. The only problem I have is that the add-on does not save my feeds when exiting the browser and opening it again, so I have to always import the feed. That aside, I look forward to what the developer does with it.