For mobile, tablets and laptops with high-resolution displays we'll want double-resolution or SVG versions of the icons served. Attached screenshot taken in Firefox 16 nightly with acceleration disabled on MacBook Pro Retina. Looks about the same in Safari.
The current icons appear to be PNG, with a PSD source file that's at low resolution. If the layers are vector shapes this should be easy to convert to high-resolution, but I don't have Photoshop on this machine to double-check.