FortAwesome/Font-Awesome — pull request #3424 by thedigitalman (2014-05-15 16:52:00+00:00)
Title: Update _spinning.scss

Opera 12.10 supports unprefixed CSS animations, gradients, transforms, and transitions or will use -webkit.
Firefox 16.0 supports unprefixed CSS animations, gradients, transforms, and transitions.

Source: https://developer.mozilla.org/en-US/docs/Web/CSS/transform