Due to the upcoming deprecation of XUL-based add-ons, I am stopping development and support for Feed Sidebar.
The Feed Sidebar is an extension for Firefox that displays the items from your Live Bookmarks in the sidebar. It is intended to be a lightweight extension of the RSS capabilities already included in Firefox, not a completely new feed management system.
Installing the Feed Sidebar will add a new sidebar to Firefox that, when opened, will display the unread items from the feeds that you have bookmarked in Firefox. Clicking on an item will show a preview in the bottom of the sidebar, and double- or middle-clicking will open the item in the browser and remove it from the sidebar.
You can choose to have the sidebar continue displaying items you've already read. If you do, these items will appear grayed out. If all of the items in a feed have been read, the feed title will be grayed out as well.
The Feed Sidebar will continue to check for new items when the sidebar is closed and will notify you when new items are found. As of version 3.0, it also has offline support, so you can read all of your feeds even if you have no Internet connection.
The Feed Sidebar toolbar contains buttons to open all items in tabs, mark all items as read, change the number of days of items to show, stop the current feed update, force a feed update, change the update interval, and hide/show the search bar. In addition, the context (right-click) menu will allow you to mark individual items as read/unread, mark an entire feed as read, open the items from a single feed in tabs, unsubscribe from a feed, and open the Feed Sidebar options dialog.
The Feed Sidebar uses its own history to track read items, so you can clear your browser history without also clearing your feed history.
Note: If you are using Sage or some other feed reader that can export its feeds in OPML format, you can import that OPML to use with Feed Sidebar by installing the OPML Support Firefox extension: https://addons.mozilla.org/en-US/firefox/addon/2625