Drop-down menu background image not working

[liunx]

On this (<!-- m --><a class="postlink" href="http://www.fgcomics.com/tester.php">http://www.fgcomics.com/tester.php</a><!-- m -->) page, there is supposed to be a small, faded image in the bottom left corner of the drop-down menu (when activated), but it instead does looks differently, by beveling in around the edges (using Firefox).

Style:

/* Drop-down skin changer background */
.skinchanger_bg {
background-attachment: fixed;
background-image: url(<!-- m --><a class="postlink" href="http://www.fgcomics.com/images/layout/skin_changer_bg.gif">http://www.fgcomics.com/images/layout/s ... ger_bg.gif</a><!-- m -->);
background-repeat: no-repeat;
background-position: left bottom;
}


Menu code (With form):

<form name="form1">
<select name="skinz" class="skinchanger_bg" onChange="changeSkin">
<option value="-1" selected>--Choose a skin--</option>
<option value="document.cookie='style=1';">Blue</option>
<option value="document.cookie='style=2';">Red</option>
<option value="document.cookie='style=3';">Green</option>
</select>
</form>