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
Merge pull request #89 from peili/patch-2

 FireFox supports range sliders as of version 23
Merge branch 'upstream'