Well, 9 is finally up and running after some difficulty with the initial build. However, it's also having some real trouble being stable -- it crashes with only minimal use and I strongly suspect the new garbage collector. However, part of the plugin IPC stack also appears in affected backtraces (yes, with plugins off). I'm trying to debug this, but it's failing in subtle and unrepeatable ways.
If I am unable to solve the stability issue by next week, we will issue an 8.0.2 beta with the new features scheduled for 9 and decide what to do at that point. The ESR is not far away (Mozilla's extended service release, to replace 3.6), so that could give us an out. More soon.