mozilla has strange border on left and bottom of window

[Bret Hughes]

we use a frameless browser window to display content on a display and
load new pages via a shell script.

in FC1, mozilla has a single pixel light colored border on the left and
bottom of the window. I don't see this in galeon but I can't control
aoeon like I can with Moz.  Does anyone have any idea what causes this? 
I have never seen this before.  It is not the window manager since it is
there even with no wm.

Bret