I'm having lots of problems as well making the editor work properly/as advertised in firefox 2.0.1. It is quite obvious to me now that this thing hasn't been properly tested. Switching to IE7 does not seem to help either. Considering this is the first time I load wordpress in that browser, I think we can safely assume it is not a browser caching problem. I haven't touched any settings in IE7 for the simple reason I only use that browser to run windows update (i.e. I've launched into it twice so far since upgrading a few weeks ago).
I've deleted all files except for uploads, configuration and two plugins (google analyticator and open id delegation) that are non editor related. So obviously that is not the issue either.
So when cache and installation seem to be fine and others are also experiencing issues my conclusion becomes that the problem is not on my side.
Finally, spellchecking is pointless considering firefox 2.0 already ships with spellchecking included and the fact that many users blog in different languages than english. Additionally many users of other/older browsers install browser addons to add spellchecking which obviously conflicts with a website overriding this. Therefore this should be an optional feature (default disabled) or a plugin.
Rather than continuing whining about it, maybe a 2.1.01 with the old editor would be a more appropriate solution for the moment until the new editor has been properly tested and fixed. IMHO this should be released ASAP before more users run into these problems. Alternatively, 2.1 could be unreleased with a nice apology/explanation on the blog.
Stuff like this happens, I'm not blaming anyone and just want to get things fixed.