#3398 Background images on left and right boxes in Firefox

[Trails]

In Firefox 1.0.4, some of the background corner images
seem to be misaligned by 1px.

The following code on line 35 of base.css seem to cause
this (though it shouldn't cause this).

margin: .8em;

As far as I can tell this seems to result from a
browser bug. I'm not sure if this is Firefox specific,
or applies to all of Gecko-based browsers.

I have been unable to reproduce the problem with any
other value in place of the .8em