I found two relevant threads (Thanks for the authors):
(1) To turn editing off use "document.frames.objContent.DOM.designMode = 'Off'".
To turn it back on use "document.frames.objContent.DOM.designMode = 'On'"
(2) var oEditor = FCKeditorAPI.GetInstance('FCKeditor1');
I don't know where and how to implement (1) but I can implement (2) successfully. The editor is disabled with greyed out text and freezed scrollbar. However, this "disabled" effect is not what I expect. I want (i)the text remains its original colors, especially the background color is or close to grey, and (ii)the scrollbar is enabled for read-only. Please advise. Thanks a lot!