Safe Button Firefox – after changing quantity – does not appear

The save button only pops up when the bottom of the screen is clicked. In Chrome it works when I use the arrows to change quantity: https://www.screencast.com/t/gilfdsBuYwxf – Using Firfox it doesnt work and the safe bottun only appears when changing the quantity manually and then clicking on the bottom of the screen. It would be great, when the “safe-button” would appear at any time…or at least when changing the quantity with the arrows. Is there any solution? Thanks for your help.