A few things I have noticed:

Corrections to CuteEditor Buttons and Menus in dev manual

TableDropDown should be table
Form should be InsertForm
Links should be LinkTree
PasteAsHTML is missing
Justify None is there twice because one should be Justify Full

In the dev manual you use the following line:
dropdown.Items.Add("<span style='font-size:18pt'>5 </span>(18pt)", "5 (18pt)", "5")
The HTML in the above line is rendered only as text and not HTML so the span tag should not be here.

Zoom dropdowns do not appear in Firefox