Index: /CKEditor/trunk/CHANGES.html
===================================================================
--- /CKEditor/trunk/CHANGES.html	(revision 5834)
+++ /CKEditor/trunk/CHANGES.html	(revision 5835)
@@ -50,4 +50,5 @@
 		<li><a href="http://dev.ckeditor.com/ticket/6097">#6097</a> : The bookmarks now use the right name.</li>
 		<li><a href="http://dev.ckeditor.com/ticket/5717">#5717</a> : Removed the scayt_contextMenuOntop setting and the SCAYT context menu options are always on top.</li>
+		<li><a href="http://dev.ckeditor.com/ticket/5956">#5956</a> : [FF] It was impossible to create an editor inside an hidden container.</li>
 	</ul>
 	<h3>
Index: /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 5834)
+++ /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 5835)
@@ -413,6 +413,6 @@
   							'></iframe>' );
 
-						// #5689 Running inside of Firefox chrome the load event doesn't bubble like in a normal page
-						if (document.location.protocol == 'chrome:')
+						// Running inside of Firefox chrome the load event doesn't bubble like in a normal page (#5689)
+						if ( document.location.protocol == 'chrome:' )
 							CKEDITOR.event.useCapture = true;
 
@@ -431,9 +431,32 @@
 							});
 
-						// #5689 Reset adjustment back to default
-						if (document.location.protocol == 'chrome:')
+						// Reset adjustment back to default (#5689)
+						if ( document.location.protocol == 'chrome:' )
 							CKEDITOR.event.useCapture = false;
 
+						// The container must be visible when creating the iframe in FF (#5956)
+						var element = editor.element,
+							isHidden = CKEDITOR.env.gecko && !element.isVisible(),
+							previousStyles = {};
+						if ( isHidden )
+						{
+							element.show();
+							previousStyles = {
+								position : element.getStyle( 'position' ),
+								top : element.getStyle( 'top' )
+							};
+							element.setStyles( { position : 'absolute', top : '-3000px' } );
+						}
+
 						mainElement.append( iframe );
+
+						if ( isHidden )
+						{
+							setTimeout( function()
+							{
+								element.hide();
+								element.setStyles( previousStyles );
+							}, 1000 );
+						}
 					};