Last year it was understood that Mozilla would be running the Firebird engine by now. That has not happened. Information on the Mozalline Forum indicates that there is no firm schedule for the conversion.
Support for the Mozilla Suite has been extended. Mozilla 1.6 was supposed to be the last. The roadmap has been extended to include a version 1.7.
Download of 1.6 release candidate is expected this week with final release in early January.