Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 4174)
+++ /CKEditor/trunk/CHANGES.html	(revision 4175)
@@ -56,4 +56,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/3438">#3438</a> : Floating panels are off by (-1px, 0px) in RTL mode.</li>
 		<li><a href="http://dev.fckeditor.net/ticket/3370">#3370</a> : Refactored use of CKEDITOR.env.isCustomDomain().</li>
+		<li><a href="http://dev.fckeditor.net/ticket/4230">#4230</a> : HC detection caused js error.</li>
 	</ul>
 	<h3>
Index: /CKEditor/trunk/_source/core/_bootstrap.js
===================================================================
--- /CKEditor/trunk/_source/core/_bootstrap.js	(revision 4174)
+++ /CKEditor/trunk/_source/core/_bootstrap.js	(revision 4175)
@@ -23,5 +23,14 @@
 
 	// Update CKEDITOR.env.
-	if ( ( CKEDITOR.env.hc = ( hcDetect.getComputedStyle( 'background-image' ) == 'none' ) ) )
+	// Catch exception needed sometimes for FF. (#4230)
+	try
+	{
+		CKEDITOR.env.hc = ( hcDetect.getComputedStyle( 'background-image' ) == 'none' );
+	}
+	catch (e)
+	{
+		CKEDITOR.env.hc = false;
+	}
+	if ( CKEDITOR.env.hc )
 		CKEDITOR.env.cssClass += ' cke_hc';