It seems mozilla the web application suite as it stands today is coming to an end with version 1.4. Phoenix, Thunderbird will replace the mozilla navigator and and mail applications. The rest of the suite will be add-on based or separate applications; this means parts such as editor(composer), Venkman, DOMInspector etc.
This is a major restructuring they are talking about.
Also, of interest for us standards freaks, they will be reworking it to easily tap in new experimental standards implementations in a modular way.
(Five year anniversary, 200 000th bug rapported, and now this. Much new about mozilla this month, so far.)