When customizing colors of the chrome, I have not been able to find a way to customize the color of the visual focus indicator. The best hack I've been able to come up with is to try to create a secondary outline, but the regular focus indicator draws over it. In this example the buttons are:

1. Default behavior
2. Hack dotted outline
3. Hack solid outline (black focus indicator overlays to look dotted)

I would think -moz-focus-outer and -moz-focus-inner would affect something, but they don't seem to.