Make sure that mousing over XUL elements results in no trigger of a mouseleave. Fixes #6013.

src/event.js

@@ -604,17 +604,12 @@ var withinElement = function( event ) {
 	// Check if mouse(over|out) are still within the same parent element
 	var parent = event.relatedTarget;
 
-	// Traverse up the tree
-	while ( parent && parent !== this ) {
 	// Firefox sometimes assigns relatedTarget a XUL element
 	// which we cannot access the parentNode property of
 	try {
+		// Traverse up the tree
+		while ( parent && parent !== this ) {
 			parent = parent.parentNode;
-
-		// assuming we've left the element since we most likely mousedover a xul element
-		} catch(e) {
-			break;
-		}
 		}
 
 		if ( parent !== this ) {
@@ -625,6 +620,8 @@ var withinElement = function( event ) {
 			jQuery.event.handle.apply( this, arguments );
 		}
 
+	// assuming we've left the element since we most likely mousedover a xul element
+	} catch(e) { }
 },
 
 // In case of event delegation, we only need to rename the event.type,