Index: /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js
===================================================================
--- /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 7430)
+++ /CKEditor/trunk/_source/plugins/wysiwygarea/plugin.js	(revision 7431)
@@ -780,12 +780,12 @@
 								if ( CKEDITOR.env.gecko )
 								{
-									var scroll = domWindow.getScrollPosition();
+									var body = domDocument.getBody();
+
 									// Page up/down cause editor selection to leak
 									// outside of editable thus we try to intercept
 									// the behavior, while it affects only happen
 									// when editor contents are not overflowed. (#7955)
-									if ( !scroll.y )
+									if ( domWindow.$.innerHeight > body.$.offsetHeight )
 									{
-										var body = domDocument.getBody();
 										range = new CKEDITOR.dom.range( domDocument );
 										range[ keyCode == 33 ? 'moveToElementEditStart' : 'moveToElementEditEnd']( body );