Q: Internet explorer and mozilla rgba css3 problem I have this css style:
    background:#000;
    background:rgba(0,0,0,0.7);
    background: transparent;
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000)"; /* IE8 */    
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000);   /* IE6 & 7 */      
    zoom: 1;

It works great in internet explorer, but i have to keep the  background: transparent; style. If i keep it, mozilla makes my background transparent
Any ideeas?

A: Learn to deal with IE quirks using IE Conditionals:
http://www.quirksmode.org/css/condcom.html
<style type="text/css">
.stuff {
  background:#000;
  background:rgba(0,0,0,0.7);
}
</style>

<!--[if IE]>
<style type="text/css">
.stuff {
  background: transparent;
  -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000)"; /* IE8 */    
  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000);   /* IE6 & 7 */
  zoom: 1;
}
</style>
<![endif]-->

<div class="stuff">Stuff</div>

jsfiddle demo: http://jsfiddle.net/cYtKJ/1/
EDIT
You could also use it to import different style files:
<link rel="stylesheet" type="text/css" href="style.css">
<!--[if IE]>
<link rel="stylesheet" type="text/css" href="style-ie.css">
<![endif]-->

You just have to be careful to put the style-ie.css last if it's overriding other css commands.

A:     background: transparent;
    background:rgba(0,0,0,0.7);
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000)"; /* IE8 */    
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr=#B2000000,endColorstr=#B2000000);   /* IE6 & 7 */      
    zoom: 1;

Problem solved.
However, there might be issues in IE9, since it supports RGBA too. 
So probably the best solution is to use conditional comments or just a solid color fallback in non-RGBA browsers.
