6 and 7 will include other improvements and features which can be discussed elsewhere. Mozilla will release a new major version every 6 weeks.
I found it very jarring to read that Firefox 6 isn't out yet, but the thread talks as if Firefox 8 is actually out, or very close to being released. In my mind I'm envisioning a weird, staggered, neither increasing nor decreasing of version number release cycle.
I think you're coming from a different angle where all of this is very familiar for you, so you can't relate to the confusion some of us other readers have had to deal with.