Firefox's Live Bookmarks feature does a fine job of keeping track of RSS feeds. Feed Sidebar is a free add-on that opens feeds in a sidebar equipped with a handy toolbar that makes it easy to search and sort feeds, mark them as read, and limit their age. It doesn't replace Live Bookmarks in Firefox; it augments the standard tool. But if you follow a lot of feeds, you'll like what it adds.
After a quick and trouble-free external download, we restarted Firefox. We clicked the RSS button on the toolbar, and clicked Feed Sidebar's left-hand sidebar that we could drag to resize as well as toggle open and closed. A folder labeled Latest Headlines displayed the most recent 60 headlines; clicking it expanded the view, with individual feed data displayed below.
Feed Sidebar's toolbar makes the difference. From it, we could Open All In Tabs (we recommend it with smaller folders with fewer feeds, obviously) as well as Mark All as Read, Reload Feeds in increments of 10 minutes to 5 hours, sort by name or date, and Limit the age of feeds by a range of dates up to a month. A search field beneath the controls is handy for large lists of feeds. Finally, an All button showed both read and unread items, as we liked.
We clicked a headline, and the story opened in Firefox. Right-clicking the entry in Feed Sidebar let us open, mark, and copy the feed in various ways, including unsubscribing. Feed Sidebar's options include basic settings such as updates and pop-up notifications and a Featured Feeds tab that includes several free feeds you can visit to help pay the bills, including one that lets stouthearted users look inside Conan O'Brien's head via his Twitter feed.
Sidebars add a lot of capability to Firefox. Feed Sidebar could be extremely helpful for Firefox users who follow more than a few RSS feeds.