Remove the box around the icon when minimize

[Javier Caneiro]

I look these screenshots and I want to know how eliminate the box of the
icons when they are minimized. Some examples:

http://www.plig.org/xwinman/screenshots/xfce-default.jpg
http://heuy.hp.infoseek.co.jp/html3/xfce/scshot-big.jpg
http://jjnet.prohosting.com/linux/screenshots/entornos/desktop-xfce-mozilla-moden-2.jpg

Thanks

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 / \  / _/  \   Javier Caneiro (McGyver) <mcgyver at telecable dot es> 
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