It looks like Mozilla is pushing the envelope on what's possible with the Web browser:

Conversing (a.k.a. messaging) is a common online activity, and a number of desktop and web applications enable it.  But with an increasing variety of protocols and providers, it’s getting harder and harder to keep track of all your conversations.

Could the web browser help you follow and participate in online discussions?

Snowl is an experiment to answer that question.  It’s a prototype Firefox extension that integrates messaging into the browser based on a few key ideas:

  1. It doesn’t matter where messages originate. They’re alike, whether they come from traditional email servers, RSS/Atom feeds, web discussion forums, social networks, or other sources.
  2. Some messages are more important than others, and the best interface for actively reading important messages is different from the best one for casually browsing unimportant ones.
  3. A search-based interface for message retrieval is more powerful and easier to use than one that makes you organize your messages first to find them later.
  4. Browser functionality for navigating web content, like tabs, bookmarks, and history, also works well for navigating messages.

Currently, Snowl is available in prototype form where only two messaging sources are supported, RSS/Atom and Twitter. Still, it's really interesting looking. Check out the full blog post for more info and screenshots.