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 (...)

Password Exporter is an extension for Mozilla Firefox and Thunderbird that allows you to export and import your saved passwords and disabled login hosts from Password Manager.

The logins will be exported to an XML (Extensible Markup Language) or CSV (Comma Separated Values) file and can then be imported into another application or computer that has Password Exporter installed.
Password Exporter (...)