Characteristics Dropdownt not showing

-- url of the page with the problem -- : beautiful-spirit.com/index.php/en/incens...-use-this-for-orders
-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.6.5 Stable
-- PHP version -- : 5.6.29
-- Browser(s) name and version -- : Firefox 50.1.0 Linux

Hi,

I need to enable selection of various product quantities, where the price is not a straightforward multiplication.
(i.e. the more you order the lower the total price drops).

I defined a new Characteristics item called quantity. In it, I defined 5 quantities and defined Characteristics selection method as "Dropdown".
Next, in my product, under "Specifications => Characteristics" I declared a new characteristic "Quantity" with a default for lowest quantity.
Then, I defined product variants, with the 5 different quantities and their prices.

The dropdown list simply doesn't show.
See: https://beautiful-spirit.com/index.php/en/incense-and-resources/product/palo-santo-test-product-don-t-use-this-for-orders
(If you get a 404 error, please do a shift+reload. I'm having a weired problem there)
If I change the Characteristics selection method to "Radio Button" - it does work (but looks ugly and very confusing. Certainly not the right choice).

Am I doing something wrong? (I tried looking for a conflicting css declaration but couldn't find any).

My other option is defining the quantities as options. I then get a dropdown list, but that is the very wrong way to do this, because options only specify the addition of the price, not the price itself. In addition to that, options don't change the product title to reflect the selection, which is also not good.
See: https://beautiful-spirit.com/index.php/en/incense-and-resources/product/%D7%9E%D7%A7%D7%9C%D7%95%D7%AA-%D7%A2%D7%A5-palo-santo

Thanks in advance,
Ben

Thank you so much Nicolas,

I fixed it!

Also, I now see that I wasn't able to detect it with firebug. You used Chrome developer tool.
So sometimes it's better to try use both tools to cover everything.