I went through the whole uninstall process and added the new editor to replace this WYSIWIG but instead of having a new editor to try out, I was left with no WYSIWIG whatsoever and no place to add content. (Firefox 2.0, Joomla 1.0.15)
Reinstalling JoomlaFCK resolved the issue, but apparently I'm stuck with it.
I'm not entirely upset as its still a great product.
You only need to update Joomla!'s Global Configuration and set the JoomlaFCK as default. We also have tutorial that would have walked you thought the changes.