sifr and thickbox conflict in FF Ubuntu, with hacky patch

I'm not sure exactly how to classify this because I'm not sure exactly what's going on. It's basically the same problem as here: http://drupal.org/node/134551

For me, sifr headers were falling behind the semi-transparent layer of thickbox as they should on FF and IE6 in windows, but not with FF in Ubuntu. The fix mentioned in the link above didn't work.

The frontmost layer in Thickbox, the one with the image, didn't have this problem, so I started copying css attributes from that layer to the semi-transparent one. The overflow attributes made the sifr flash bits disappear when Thickbox was on top, which for me is better than appearing on top, so I went with it. This is by no means a fix, but I thought, if other people are having this problem, this may be a clue.

Here's the css I added to my theme's css:

/* sifr and thickbox conflict patch hack */
.TB_overlayBG{
overflow-x:auto;
overflow-y:hidden;
}