ging/licode — pull request #89 by peili (2014-02-11 16:52:36+00:00)
Title:  FireFox supports range sliders as of version 23

Volume bar uses "-webkit-appearance: slider-vertical;" , but FF doesn't support it. Firefox support orient="vertical".

Also check: http://stackoverflow.com/questions/15935837/how-to-display-a-range-input-vertically