Bug 1095832 - [RTL][Video] Progress slider position moves opposite from ...

...slider progress
Punam used this same code in a gallery patch and there, I suggested that it would be easier to read without a two-line conditional. Maybe something like this would be cleaner:

var startEdge = navigator.mozL10n.language.direction === 'ltr' ? 'left' : 'right';
dom.playHead.style[startEdge] = percent;