Mozilla Firefox guys have redefined the release plan a bit. Firefox 3.7 is to be merged with 3.6 line as the features are almost complete and focus on out-of-process plugins. So, now we have Firefox 4.0 line with other changes. The focus is on speed.
See Firefox presentation here or get the 4.0 beta 1 candidates from here.
Edit: Wow, the startup is faster than current Dev version of Chrome. Even without Firefox Preloader! This is definitely my new default web browser and HTML viewer.