Can I specify the number of lines a dropdown/combo box displays when it is open?

I have a dropdown box that contains 12 options. When it is in its open state on the form, it on;y displays the first nine lines, and the last three are in an "overflow:scroll" kind of state, and unfortunately—and I don't know if this is platform- or system-specific—the  only way to scroll them is to physically click on the scroll bars at the side of the dropdown box, and drag them downwards. It's not possible to use a two-finger scroll gesture as I usually can.

It's a first-world problem, I realise, but it does interrupt the user interface flow, and I wonder if there is a javascript way of specifying more lines of text should be displayed before it needs to add scroll bars.

(I've checked the preferences and drawn a blank, but if there is one that I've missed, that would be a perfectly acceptable answer too!)

Many thanks for your time,

NathanG