Here is how iteration 14 of the new Firefox icon would appear in context on mozilla.com, XP, OS X and Vista. I’ll try to get some Linux images posted as soon as we have a patch ready.
The reflection line featured in this iteration gives the globe a bit more gloss and dimensionality. It also helps to establish two contrasting textures in the icon, making the refresh really more about fidelity of detail as opposed to more significant structural or color palette changes. This type of reflection line is also consistent with common textures and lighting found in Vista and OS X, and blurs out at the smaller XP-sized resolutions.
Note: the shadow being clipped off at the top of the icon is actually being drawn by OS X, and isn’t really something we can directly control (aside from making the icon visually smaller).