Mozilla Messaging, citing Mozilla's increased focus on Web-borne communications, will be reintegrating with Mozilla Labs.
The Messaging subsidiary was formed in 2008 to focus on Thunderbird, but given Mozilla Labs' current focus on identity and contact management, it now makes sense for the groups to be merged. Thunderbird will be unaffected by the change -- some URLs might change, but that's it -- and presumably Messaging's F1 and Raindrop will thrive in the Labs playground.
What this means for the end user -- for the hundreds of millions of Firefox users -- is that the next big additions will be communication- and messaging-oriented. Contacts and F1 will be almost certainly be baked into Firefox 5 or 6, both of which will be released this year -- and, who knows, there might be something else even more exciting up Mozilla Labs' sleeve!