Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 4491)
+++ /CKEditor/trunk/CHANGES.html	(revision 4492)
@@ -59,4 +59,5 @@
 		<li><a href="http://dev.fckeditor.net/ticket/3373">#3373</a> : Fixed empty context menu when there's no menu item at all.</li>
 		<li><a href="http://dev.fckeditor.net/ticket/4473">#4473</a> : Fixed setting rules on the same element tag name throw error.</li>
+		<li><a href="http://dev.fckeditor.net/ticket/4514">#4514</a> : Fixed press 'Back' button breaks wysiwyg editing mode.</li>
 	</ul>
 	<h3>
Index: /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 4491)
+++ /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 4492)
@@ -641,4 +641,28 @@
 		}
 	});
+
+	// Fixing Firefox 'Back-Forward Cache' break design mode. (#4514)
+	if( CKEDITOR.env.gecko )
+	{
+		var topBody = new CKEDITOR.dom.element( window.top.document.body );
+		topBody.setAttribute( 'onpageshow', topBody.getAttribute( 'onpageshow' ) 
+				+ ';event.persisted && CKEDITOR.tools.callFunction(' +
+				CKEDITOR.tools.addFunction( function()
+				{
+					var allInstances = CKEDITOR.instances,
+						editor,
+						doc;
+					for( var i in allInstances )
+					{
+						editor = allInstances[ i ];
+						doc = editor.document;
+						if( doc )
+						{
+							doc.$.designMode = 'off';
+							doc.$.designMode = 'on';
+						}
+					}
+				} ) + ')' );
+	}
 })();