Firefox 3.6.13 doesn't open new tab with open(..., "_blank")

This was my code, what should I do to open a link in a new tab in Vaadin?
The code works, it just opens in the same tab which is wrong.
I mention this code is in a ClickListener of a Button, with or w/o setStyleName(BaseTheme.BUTTON_LINK), it does the same

String appURL = getApplication().getURL().toString();
				ServletContext sc = ((WebApplicationContext)getApplication().getContext()).getHttpSession().getServletContext();
				String appContextPath = sc.getContextPath();
				getApplication().getMainWindow().open(
						new ExternalResource(appURL.substring(0,
								appURL.lastIndexOf(appContextPath)) + "/jforum", "_blank"));

Picked up this answer from link below

https://vaadin.com/forum/-/message_boards/view_message/852623#_19_message_855439

String appURL = getApplication().getURL().toString();
				ServletContext sc = ((WebApplicationContext) getApplication()
						.getContext()).getHttpSession().getServletContext();
				String appContextPath = sc.getContextPath();
				getApplication().getMainWindow().executeJavaScript("window.open('" + (appURL.substring(0,
						appURL.lastIndexOf(appContextPath)))
						+ "/jforum" + "', '_blank')");

EDIT: actually this should be the production URL I think (in the way it is above it doesn't work in production - it still opens in the same tab when opened from elsewhere.):

getApplication().getMainWindow().executeJavaScript(
						"window.open('" + "http://lottomerc.com" + "/jforum"
								+ "', '_blank')");