Error messages recorded in the JavaScript console of Firefox 1.0

These error messages are after add or change:
Error: uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLDocument.designMode]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: http://localhost/myed/js/dhtmleditor/htmlarea.js :: initIframe :: line 742"  data: no]
Error: uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLDocument.designMode]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: http://localhost/myed/js/dhtmleditor/htmlarea.js :: initIframe :: line 742"  data: no]
Error: uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLDocument.designMode]"  nsresult: "0x80004005 (NS_ERROR_FAILURE)"  location: "JS frame :: http://localhost/myed/js/dhtmleditor/htmlarea.js :: initIframe :: line 742"  data: no]

These error messages after cancel add
Error: this._doc has no properties Source File: http://localhost/myed/js/dhtmleditor/htmlarea.js Line: 1782
Error: this._doc has no properties Source File: http://localhost/myed/js/dhtmleditor/htmlarea.js Line: 1782

