Java Web Start Applet opening new Browser Window/T

Question

Having successfully migrated an applet to a java webstart applet, I notice that every call to

getAppletContext().showDocument(
new URL("http://"+ host+ "/" + filename + language + ".htm"),
 "Helppage");

opens a new browser window (Win 7/MSIE11) or tab (firefox depending on configuration) though I obviously request a specific named possibly already open browser window.

Has anyone successfully managed to redirect those calls to one browser window (tab)? If yes, how?

Looks a similar context to How do I close a browser window that was opened by Java Web Start

• Thanks in advance