I have cPanel through my hosting and upgraded to version 2.8 today to quickly find that I could not use the editor, among other known bugs. I upgraded to the Beta 1 version. Back-up everything, removed the wp-admin and wp-includes folders and FTP-ed the new files up.
Testing in a W2K system with Firefox, the editor works. Trying to post on a Fedora 8, Firefox 2 (firefox-2.0.0.16-1.fc8) system shows the same error as the 2.8 original install. The TinyMCE editor does not respond and types white text.
Hope this helps.
Jason