Rated 4 out of 5 stars
This is the best feed reader add-on for Firefox simply because I don't need to squint to read the feed list and Firefox retains control of the zoom settings in the article pane.
Other add-ons either fail in other areas - like Sage, which could have been the best - while others could have been decent if feed lists and/or articles weren't unreadable due to font-size.
The only thing that keeps Feed Sidebar from being close to perfect is not being able to sort feeds into folders or groups (see Sage.)
Being able to sort feeds by name, date or most recently updated is fine, but unless users could rename feeds (to use with the sort-by-name option), they have to skim through all their feeds if they want to read only those on a specific subject. (And the more feeds a user has, the worse this becomes.)
(I thought I could workaround this by moving my feeds into a single bookmarks folder and arranging them in a specific order, but no luck.)
I'd like to give this add-on 4 and 1/2 stars, but since I can't I'll give it 4. If the single problem it has is fixed it'll automatically get 5 stars from me!