Bug on checkout in same cases in Firefox and IE

-- HikaShop version -- : 2.3.5
-- Joomla version -- : 3.3.6
-- PHP version -- : 5.3.13
-- Browser(s) name and version -- : firefox 35.0.1, IE 11.0.9600.17498

Firefox, IE:
If user register or login on checkout page: then he choose payment metod (or shipping or address) hikashop on my site create order (user don't press submit button).
If user after what press submit button, he get error "cart empty"

Safari, Chrome:
All work correctly.

I spend 3 day to find reason this behavior:
File /components/com_hikashop/controllers/checkout.php.
Bug code:
if(!JRequest::getVar('hikashop_validate',1)){ //default value - hikashop_validate=1!!!! hikashop_validate - is ID
return false;
}
Correct code:
if(!JRequest::getVar('validate',0)){ // validate - is NAME
return false;
}
Now it work on Firefox, IE, Safari, Chrome.