Hello Moshtafizur,
I have the problem whether it’s on Firefox (logged in as admin or not), as well as on chrome.
In fact, the problem I encounter is on the basket page, if the desired number of a product does not exist in the parameters that we entered previously, then the basket page breaks..
Example with my configuration, if I add once 100, then once 60, that makes 160 and is not planned in my base dropdown. And it breaks the cart page every time.
I don’t know if I’m clear enough?
It is possible to test here: http://s775888136.onlinehome.fr/preprod-saciso/produit/fresh-paper-pack-copie/ by adding to the basket once 100, then once 60