Wizz RSS News Reader is an excellent RSS Firefox extension where you can open it as a sidebar with a customizable shortcut key. You can organize your news feeds into categories and channels. The other reason that I like most is without the hassle of logging onto any account to read the feeds, it is browser based(only for Firefox), whenever I want it, just with a touch of Alt+Q key, toggle it to shut it down, what a breeze to use! If you are the one who tend to use different PC to browse the net, you can always sign up an account to save your feed list on the their server, which you can then access the feeds from any PC.