CSS Sprite doesn't work in firefox

[programAngel]

if you see the following link in chrome:
http://barzilaymor.co.il/diurplus/DiurPlus.php

you will see in every rectangle, 4 small rectangles in the color blue, orange, green and red.

But in firefox you see none of them.

I have used CSS Sprite to create them and here is the code:

<img src='' class='rectangular-key extra-info-key'/>
<img src='' class='rectangular-key galley-key'/>
<img src='' class='rectangular-key contact-key'/>
<img src='' class='rectangular-key map-key'/>

and the css:

.rectangular-key{
    width: 10px;
    height: 10px;
    background:url('image/strip.png');
}
.extra-info-key{
    background-position: -304px -135px; 
    border:0;
}
.galley-key{
     background-position:  -304px -152px;
      border:0;
}
.contact-key{
        background-position:  -304px -118px;
         border:0;
}
.map-key{
     background-position: -304px -169px;
      border:0;
}

what is wrong here?

After all it is working well for me in IE and chrome, so what should I do in order to make it work for firefox?