Some may remember a project of mine - Feed-O-Matic. It was a Firefox extension to read RSS feeds. It was going ok, but I've now found Sage for Firefox, which basically does what I was trying to do.
The features that I wanted aren't all present but most of them are in Bugzilla. Hopefully they should see the light of day soon. But even so, if you want to keep track of multiple fast-moving sites, Sage for Firefox is fantastic.