Hi,
My only suggestion will be to not use the popup for the "add to cart".
HikaShop have two kinds of popup, the classical (for the content) and the images (for, the images).
Shadowbox is a lightbox, it just work for images.
For the content, we are using for most of them the setting ; except for the "add to cart" popup which is forced to use mootools squeezebox ; but we are currently working on it with the refactoring of the checkout system.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.