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
* Feed Discovery
* Integrates with Firefox's bookmark system
* Imports and exports OPML feed lists
* Newspaper feed rendering customizable via style sheets
* Support for the following locales: Argentine Spanish, Catalan, Chinese, Czech, Danish, Dutch, Finnish, French, German, Greek, Hungarian, Italian, Japanese, Korean, Polish, Portuguese, Russian, Serbian, Slovenian, Spanish, and Swedish