The extension Feed Sidebar by Christopher Finke is a small extension that allows to view one’s Live Bookmarks in a sidebar, much like one would view history or bookmarks. It is not a new RSS feed management, but instead operates on the live bookmarks one has in the profile via the “Subscribe to this page” option from the “Bookmarks” menu.
In the version that is currently on addons.mozilla.org, there are several problems with missing label7control associations in the Options dialog as well as problems navigating the tree, and more importantly, opening a feed article via the keyboard.
Not too long ago, I contributed a patch to the project to fix these problems, and Chris has accepted it and put it into a recent beta version of Feed Sidebar. He also made it possible to access the sorting options from the context menu.
The latest beta brings a better updating mechanism that is less resource hungry.
For those of you who have asked me about a way to view feeds in a tree like structure, this is definitely worth a try! Go download the latest beta version here! I’ve found it to be very stable and accessible. Of course, feedback is welcome! You can either contact Chris directly of course, or leave a comment here, I’ll then forward it to him.