The profile directory for Firefox will be changed (for the last time) to Mozilla/Firefox/ (from Firefox/), as Ben Goodger announced at the MozillaZine forums. This follows up on the last profile directory change from Phoenix/ to Firefox/. This also seems to mean that the profile directory for the Mozilla suite will go into Mozilla/ while having a Firefox/ directory under that (i.e. Mozilla/Firefox/) for Firefox - a little weird.
Users of the Firefox 0.8 release, don't worry, because I'm sure Ben and his team will have a neat, transparent migration script for your profiles when Firefox 0.9 comes out. You probably wouldn't have to do a thing.