Default settings need to add more padding on the sprite or let it be configurable..

[brunis]

I'm seeing icons spill into other icons in Firefox when using recommended scaling in Windows (125% in my case).
If i go and change my icons to be width and height 16 and viewport 0 0 18 18 it goes away .. (previously viewport was 0 0 16 16)
So i'd suggest you add a bit more space between the icons by default, so scaling issues and subpixel precision doesn't become an issue at different scales on different browsers.

[Kreeg]

relates to #451