http://www.mozilla.org/projects/firefox/roadmap.html
It will be based on the Mozilla 1.8 codebase; 1.8 beta 1 will be released shortly, with beta 2 in March and the final release will roughly coincide with Firefox 1.1. There are some pretty pictures showing the timeline.
http://weblogs.mozillazine.org/asa/archives/007450.html
Source: OS/2 Warp News and Rumors