I’ve got WYSIWYG editing working in my copy of Radio running with Mozilla on MacOS X. It should work with Mozilla 1.3 or greater, on all platforms.
I’m using it right now to create this post. (Cool, heh?) Here’s a screenshot.
In a lot of ways, it seems more powerful than the editor included with IE 5 and up (Windows only). For example, it’s got multi-level Undo/Re-do, and it uses inline styles to do its formatting, instead of the rather ugly HTML that IE produces.
I’m planning on releasing a beta for Radio users later today. (Don’t worry — a Manila version will be close behind, since most of the code is shared.)