One of the features that has undergone virtually no improvement is the Live Bookmarks - the RSS feed reader of Firefox. Live Bookmarks is unique but not the typical feed reader users want. If you want a more usable feed reader, use Brief.
The Brief extension is not a separate RSS feed reading tool for Firefox - it simply enhances the existing feed reader. It’s like frontend to Live Bookmarks. Brief takes all subscriptions in Live Bookmarks and presents it in a more functional and practical manner.
On the right you can see the list of subscriptions, and on the left is the expanded view of the feed selected. You can mark feed read or star important one. You can also choose a more compact view by displaying only the headlines, or viewing only the unread items or the bookmarked ones.
Brief checks feeds for updates in the background and notifies you about new items. The status bar icon shows the number of unread items.
There is a search box that allows you to quickly search through your subscribed feeds. There are also plenty of shortcuts that makes feed reading quicker and easier.
Other features include the ability to specify the time interval of feed update, and automatically removing items after a certain period of days.