Firefox 6 may have been just released, but I have to admit that versions 7, 8 and 9 may be much more interesting from the end user's point of view. Firefox 7, for example will bring the Azure 2D graphics API and memory enhancements, Firefox 8 will make add-ons much safer to deal with and we now hear that Firefox 9 is likely to get the much anticipated tablet UI. Mozilla just posted the tablet UI as a deliverable for Firefox 9.
Firefox 8 nightlies apparently integrate a first version of the UI already, even if it is not enabled and not even accessible via the about:config menu. We would expect the feature to surface over the next few weeks.
2DayBlog.com, Firefox's tablet UI scheduled for Firefox 9 integration