LiveClick is a very handy extension for Firefox (and happily, it works even with current Firefox 2 nightlies) that teaches new tricks to good old Firefox live bookmarks.
It adds Open Location and View Feed options to all live bookmarks. Open Location will open the web site you subscribed the feed from, while View Feed shows the actual web. In Firefox 2 beta it is displayed as a nicely formatted web page.
A third option can mark all items in the web feed as read. Yes, LiveClick shows which items you have already checked. You can configure how to mark read items: hide or gray out read items, darken unread items, no mark or define a custom style.
You can customize the web feeds refresh interval and ask for an alert whenever a new item is added to selected web feeds (a "Select all" button would be really handy here) and even have it autoload the new item, open the feed, the web site or do nothing.
All in all it does pretty much of what I've been missing in Firefox's default web feeds handling. Greatly recommended for every intensive web feeds user.