Can anyone help with Firefox/chrome differences?

I have just activated the quantity Drop down in my product view and since I mostly develop in chrome I thought everything was looking good.

However, I checked the page in Firefox and the dropdown and the "add to cart" button are way out of alignment in firefox.
You can see the issue in the screenshot below.

The link is:
livelaughlove.com/live-laugh-love-shop/p...heart-burnout-hoodie

Thank you, it worked. Not at first though.
Before posting I had added the same rule with no effect. However, I was doing that in firebug and I didn't think of using !important
WHen I added that to your code, immediately it worked fine along with the display: inline-block; that is already assigned to the element.

Thank you very much.