The best thing about RSS reader in Firefox for me was the fact it blended perfectly with bookmarks feature - it was easy to reach especially when you had bookmarks bar enabled. The way it displayed content also suited me - I didn't have to break my browsing flow to open another tab like in Presto-based Opera or special feed with summaries like in Safari; links in form of bookmarks changing titles were absolutely best.

A web browser today is essentially an Internet-facing client-side operating system. You are suggesting to use something that runs outside this OS. (Just pointing out.)

Nothing's "wrong" with it, but I have yet to find one that allows me to read more headlines in a shorter time than Live Bookmarks.