I really hope Firefox people will reconsider this proposed versioning system. It's seriously reducing information related to stability and major architectural changes. And for what? So that Firefox plays catch-up with other browsers? It certainly doesn't mean more work is being put into it and it certainly doesn't help setting realistic goals.
It's really good to see a move towards releasing more often, but messing up with the versioning scheme in this way is bad. Other projects are able to keep up with similar goals without resorting to such tricks. Just release when something gets done, not just because a few months have passed.
Maybe the problem lies in merging too much too soon? Maybe those features should stay out of the main tree until most issues/bugs have been ironed out? I don't know, I'm not involved in Firefox development, but perhaps there are better solutions to this problem.