Unfortunately some influential sites and UI designers have lately been trying to improve on the standard scrollbar , often in an attempt to make them work better for very small screens and/or touchscreen devices. IMHO, their changes have mostly been steps backwards as far as traditional mousing is concerned. The scrollbar is old and highly evolved. It's not immediately obvious that it can be improved. I suspect it will be with us until we eliminate scrolling itself.
In Firefox and Opera, the arrow buttons are showing up fine for me. How are you viewing this?
I see it in chrome, not firefox.