Menu shows right in Chrome, but not in Firefox - html

Question

I'm having a problem with a nav bar in my site. It works in chrome, but something weird happens in firefox and I have no idea what it is...
In Firefox, the dark bar menu background doesn't show. It is transparent for some reason:
In Chrome is works as expected:
My sites wrapper has opacity 0.9, but I don't think this has anything to do with the menu not showing, since it shows on chrome...
Here is the HTML and CSS for my header: http://jsfiddle.net/Xdc9F/
HTML:
<div class="header">
<header>
<h1>
<a href="#">
<img src="http://i.imgur.com/z3Y7cmW.png" alt="" />
</a>
</h1>
</header>
</div>
<!-- closing header -->
<div class="menu">
<ul>
<li class="active"><span>Home</span>
</li>
<li><span>Sobre Nós</span>
</li>
<li><span>Localização</span>
</li>
<li><span>Contato</span>
</li>
</ul>
</div>
CSS:
.menu, .menu ul, .menu ul li, .menu ul li a {
padding: 0;
margin: 0;
line-height: 1;
font-family:'Capriola', sans-serif;
}
.menu:before, .menu:after, .menu > ul:before, .menu > ul:after {
content:'';
display: table;
}
.menu:after, .menu > ul:after {
clear: both;
}
.menu {
zoom:1;
height: 69px;
background: url(http://i.imgur.com/XnKK9WL.png) repeat-x center bottom;
margin-top: 100px;
border-radius: 2px;
}
.menu ul {
background: url(http://i.imgur.com/elYFBsn.png) repeat-x 0px 4px;
opacity: 1;
height: 69px;
}
.menu ul li {
float: left;
list-style: none;
}
.menu ul li a {
display: block;
height: 37px;
padding: 22px 30px 0;
margin: 4px 2px 0;
border-radius: 2px 2px 0 0;
text-decoration: none;
font-size: 15px;
color: white;
text-shadow: 0 1px 1px rgba(0, 0, 0, .75);
font-weight: 400;
opacity: .9;
}
.menu ul li:first-child a {
margin: 4px 2px 0 0;
}
.menu ul li a:hover, .menu ul li.active a {
background: url(http://i.imgur.com/jCkWOJx.png) center bottom;
display: block;
height: 37px;
margin-top: 0px;
padding-top: 26px;
color: #004f7c;
text-shadow: 0 1px 1px rgba(255, 255, 255, .55);
opacity: 1;
text-transform: uppercase;
}
I just pasted the header section, if you need the whole page code just tell me.

Answer 1

Everything works great for me. Probably you have done something wrong with the rest html or CSS.
The blue border is because of this rule:
background: url("http://i.imgur.com/XnKK9WL.png") repeat-x scroll center bottom transparent;
If you delete there isn't blue border