Transparent XUL Window in Firefox 4

I've created a Firefox extension which opens a new window and this window is transparent, means it doesn't have a background - the desktop behind it shines through!

It was done with <win开发者_如何学Godow style="background:transparent !important; -moz-appearance:none !important;">.

While it works perfectly in Firefox 3.x, I can't get any transparency in Firefox 4. The background is white. Is there any way to achieve this transparency effect in Firefox 4?

(PS: It worked on Windows only. If, after fixing it for Windows, anyone has an idea how to make it for other OSes, I would be more than happy.)

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did you include the global skin in your xul page? (<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>) Your description is typical of this skin not being imported (and I think it became required in recent firefox builds).