sage is a lightweight rss and atom feed aggregator extension for mozilla firefox. it's got a lot of what you need and not much of what you don't.
* reads rss (2.0, 1.0, 0.9x) and atom feeds* newspaper feed rendering customizable via style sheets* feed discovery* integrates with firefox’s bookmark system* imports and exports opml feed lists* support for a number of locales: argentine spanish, catalan, chinese, czech, danish, dutch, finnish, french, german, greek, hungarian, italian, japanese, korean, polish, portuguese, russian, serbian, slovenian, spanish, and swedish* simple, one step install / uninstall