Index: /FCKeditor/trunk/editor/_source/internals/fck.js
===================================================================
--- /FCKeditor/trunk/editor/_source/internals/fck.js	(revision 1066)
+++ /FCKeditor/trunk/editor/_source/internals/fck.js	(revision 1067)
@@ -57,5 +57,11 @@
 			return ( this.StartupValue != this.EditingArea.Textarea.value ) ;
 		else
+		{
+			// It can happen switching between design and source mode in Gecko
+			if ( ! this.EditorDocument )
+				return false ;
+
 			return ( this.StartupValue != this.EditorDocument.body.innerHTML ) ;
+		}
 	},
 
@@ -349,4 +355,10 @@
 	{
 		this.EditingArea.Mode = FCK.EditMode ;
+
+		// If there was an onSelectionChange listener in IE we must remove it to avoid crashes #1498
+		if ( FCKBrowserInfo.IsIE && FCK.EditorDocument )
+		{
+				FCK.EditorDocument.detachEvent("onselectionchange", Doc_OnSelectionChange ) ;
+		}
 
 		if ( FCK.EditMode == FCK_EDITMODE_WYSIWYG )