The number of feeds I am subscribed to is hurtling towards 50 and it's becoming unmanagable. At first I used the Firefox RSS Reader panel, and it was good. It wasn't perfect though - it won't do periodic updates for example. So I moved to RSS Bandit, created by Dare Obasanjo (head of XML stuff at Microsoft I believe) and Torsten Rendelmann. And that was better, but buggy and slow at times. When it worked though, it was pretty ace apart from two things - it integrates IE and it doesn't let me blog stuff I find in feeds.
So, since I have been wanting to contribute to Mozilla a little more, I'm writing my own Firefox extension to meet my needs. Blogging facility, aggregation of unread items and periodic notification of new items are on my feature list at the moment. Current state of play - it can grab the list of items from a feed and put them in an iframe on the browser window. That's an improvement for me on the RSS Reader Panel, cos the item list on that took up too much vertical space.
Anyway, I'll release it when it does the things that I want without breaking.