Many of the wordpress users are facing the problem with visual editor and editor toolbar after upgrading the wordpress 2.8 version. To resolve it please perform these steps:
1. Delete web browser cache.
2. If you are using Gears plugin in Firefox then disable it and re-enable it again.
3. Delete wp-admin and wp-includes directories and upload new copy from a fresh download from official site.
4. Visit http://yoursite.com/wp-includes/js/tinymce/wp-tinymce.php and look for any PHP errors or warnings at the top. If there are any try contacting your hosting provider to resolve them or try the next step.
6. Add define (‘CONCATENATE_SCRIPTS’, false); near the top of wp-config.php. That would make WordPress admin run slower so can try removing it in a few days and testing again.
7. We have reported success redoing the upgrade via Tools->Upgrade->Re-install automatically, then clearing the browser cache.
8. Try another browser
9. Confirm that Your Profile, “Disable the visual editor when writing”, is NOT checked.