I am a paying customer and have version 5.3 installed on my clients site.  The editor works fine for me in IE however they have reported that they cannot edit the content with IE 6.  Oddly enough I can only replicate the issue in Firefox.  When in Firefox, I have been able to update successfully once, but when the page refreshes the changes are there but none of the content is editable.  When I select 'Normal' instead of the default 'Paragraph' in the drop down menu I get the bizarre error:

Command [FormatBlock] is not supported!

Component returned failure code: 0x80004005 (NS_ERROR_FAILURE)
[nsIDOMNSHTMLDocument.execCommand]

Any help you can provide is extremely appreciated as my client is waiting for final delivery.  Please let me know if you need any additional details.

Thanks,
Jason