Not looking or working good

I have installed the JUX Mega Menu but it has two problems, I am using Firefox
1 - The webpage jumps to the side when menu item is selected
2 - I cannot access many of the menu items as I cannot click on them
I am using Joomla 3.1.5 with a Joomla51 template called Letterpress.
Test site: testasiadragon.chinesesolutions.co.uk/
Also, how can I change the style of the menu, change colours, menu sizs and visited menu items that show in white.
Please help!

Hi Simon Church,
Thanks for contacting us and choosing our product!
1. I think this issue by your site. 2 it appears the scroll bar, causing it to jerk.
2. Please go to style.css file(modules/mod_jux_megamenu/assets/css) line 99
remove z-index: 9;
3. I think you should use CSS3 Mega Menu JUX products. It has the option to change.
demo.joomlaux.com/extensions/megamenu/demo-controls.html

It is not because of the scroll bar, the whole page including the scroll bar jumps!
I tried to remove the code but still have issues.
Please can you refund me as I will not be using this extension