Tom, was there a rich text editor installed on the wiki that has been disabled? Zakilevo says that there used to be a link to switch between plain and rich text editors. Now he is stuck with the plain text editor, and no visible link to switch to the rich text editor.
More broadly, can you give us a list of extensions that we were using before, but do not appear to be compatible with the new version, so we can look for updates/replacements?
Yes, the editor is one of the extensions that broke. I'll try to make a list when I find some time.