Hi,
The dropdown looks fine to me in Firefox. Clean again your browser cache or any other cache mechanism in your computer.
https://www.dropbox.com/s/ilwfq1w7wtc2wv6/firefox_dropdown.png
The arrow in that product it’s showing to the left because it’s the last product. If you go all products to the left you will get an initial situation where the arrow is only to the right, and after that he has left/right arrows until we get to the last product only with arrow to the left.
that’s a way to know that it’s seeing the last product or else the visitor will loop through the products.
-Rui