While I may not be posting much about Firefox 4 for a few more months (after Fx 3 is released), I have gone ahead and added a Firefox 4 tag. It is likely to be released around the same time IE8 comes out (sort like the IE7 vs Fx 2 this past fall). Here are some details about Fx 4 from my Firefox Year in Review post (which is located in the Popular Posts section):
I have yet to located the code names/project names for either Fx 4 or Gecko 2. If anyone has this info let me know.