No application should depend on this feature to work cross browser right now because the CSS3 standard on page orientation for printing is still under implementation in most browsers. For Google Chrome it works just fine. Ultimately the decision of changing the orientation relays on the user during the printing process (even if it works), so you could simply let the users know that they should print the page in landscape or portrait, but in general there won't ever by a way to prevent the users from changing the orientation while printing on desktop browsers.