how to drop down the list of options in a drop down control (COMBO BOX) in a browser

Question

I've known for a long time that F4 key drops down the list in a combo box(drop down) in windows applications.

In I.E, the address box drops down if you press F4 anywhere in the page. This is NOT what I had expected, though.

However, what I want to know is, in Windows(at least), what is the key combination that will drop down the list of a drop down control(combo box) in a web browser (say, Firefox or Chrome) ?

Thank you,

Answer 1

ALT + DOWN does the trick.