Old FF needs a second parameter for getComputedStyle.

See https://developer.mozilla.org/en/docs/DOM/window.getComputedStyle
Fixing old FF which doesn't have requestAnimationFrame

So it's using setTimeout, and FF passes some value into the setTimeout callback
(See https://github.com/mootools/mootools-core/commit/3abda4139669).
Merge pull request #20 from arian/fix-old-ff

Fix old ff