Mozilla frames CSS Border

I am trying to apply a style to my frames so that regardless of browser
- it always looks *pretty much* the same (its a work thing - frames
already implemented - no choice about using frames).

Now, I found that when i apply the style to my "test" frames - it works
great - across "all" browsers. however - when i apply a
Background-color to my embedded body the frame disapears in mozilla.

Anyone seen this? know a fix?

thanks.