Sage is a lightweight RSS and Atom feed reader extension for Mozilla Firefox.
It’s got a lot of what you need and not much of what you don’t.
Sage - RSS and Atom feed reader extension for Firefox (...)

TwitterFox is a Firefox extension that notifies you of your friends’ tweets of Twitter. (former name is TwitterNotifier)

This extension adds a tiny icon on the status bar that notifies you when your friends update their tweets.
Also it has a small text input field to update your tweets.
TwitterFox - Firefox extension for Twitter (...)

Tell BlogRovR the blogs you like, and from then on, as you browse the web, Rovr instantly fetches you posts from them which link to whatever web page you’re viewing.

Rovr’s tray slides in to show you summaries of the posts about the current page. Click on a summary to read the full post, right on the page it’s about.
BlogRovR (...)