When I view your site using IE 11 set to IE 9 mode, I get a script error coming from the artisteer script.js, it gives an "access denied" message though I have no idea why. But that script failure is why part of the style is not applied such as centering the menu.
From viewing the source of your page you are NOT using the latest mojoPortal , you are using version 2.3.9.9. and it does NOT appear that you are using the latest version of our exporter plugin for Artisteer because your skin has the jquery migrate plugin enabled and this was removed in the latest plugin because it is not needed for Artisteer 4.2.
Hope that helps,
Joe