I upgraded to 2.8 last night and encountered the same problem with the visual editor being unavailable. After trying all the ideas listed here with no success, I thought I’d try to check the box in my user profile to ‘disable the visual editor when writing’. I did that, loaded the editor to confirm that it was in html mode. Then I went back into my profile and unchecked the box and tried again and the visual editor is now working in IE8 and Firefox 3.0.11.
Don
grapelog.com