Extremely minimalistic extension. The only settings that are there are a choice of two themes, and a "Feed content panel" ("Below feed list" and "Above feed list"). No OPML/XML import (I would not change the feed reader if it would require manually transferring about a thousand subscriptions). No setting for the frequency of automatic update checking. No display of the feed presence icon in the address bar. Does not add the Subscribe item to the context menu of links to the RSS feed. No language selection (if the extension supports languages ​​other than English). There is no cloud syncing of feeds via browser, nor via Google Drive/Dropbox connection.

Mozilla Firefox 140.0b1 (64-bit), RSS Sidebar 2.1.1 (21 May 2025), Microsoft Windows 10.0.19045.5854

As a long-time Sage user, this add-on looked like just what I was looking for on Firefox 57. However, right now its functionality is very limited. My biggest issue is that the reader doesn't notify you of new/unread feed items in any way. It simply gives you a list of items to click through with no way of telling whether you've already viewed them or not. I will be monitoring this add-on because it looks like it could have potential, but in its current state it's just not very useful as a feed reader.