Hi,
About the lightbox, it can be related to the popup system you use.
But you can choose the lightbox system used by HikaShop in your HikaShop configuration ; chose the "popup mode" "mootools".
www.hikashop.com/support/support/documen...html#display_general
But when I went to your checkout, I got some javascript errors in a "0a6edcad7da16597b9872823530176b6.js" file, line "3344".
Regarding the code, I don't think that is related to HikaShop but something from your template I guess (not sure, everything is obfuscated in the file).
About the speed, I will recommend you to check the plugins you got installed and activate temporally the Joomla debug mode.
In this mode you can see a lot of time markers for different events during the page generation ; it could guide you on which element should be improved.
But something, having too much plugins to "optimize" the page, slow down the page generation.
Regards,