From Mozilla Labs, an idea whose time is coming. I was struck by this bit though.

Our next step is to gather feedback on the prototype and the ideas behind it. We want to know if the concept has promise and is worth pursuing further. We’re particularly interested in feedback on how messaging might fit into the browsing experience and if there are other interfaces (or refinements to the two interfaces built into the prototype) that would make it easier for users to have online conversations.

We’re still considering what may come after that, but possible extensions to the Snowl prototype include:

• support for additional message sources, e.g. Facebook, AIM, Google Talk, etc.;
  
• an interface for writing and sending messages to enable true two-way conversations;

Since Facebook and Google Talk already support or are going to support XMPP, the only question is whether Snowl will support it too. Other chat services should just follow suit. In other words, there's no point in mentioning "additional message sources" when all of those sources use XMPP. Just mention XMPP!