Fit website background image to screen size

you can do this with this plugin http://dev.andreaseberhard.de/jquery/superbgimage/

or

   background-image:url(../IMAGES/background.jpg);

   background-repeat:no-repeat;

   background-size:cover;

with no need the prefixes of browsers. it's all ready suporterd in both of browers

Try this ,

 background: url(../IMAGES/background.jpg) no-repeat center center fixed; 
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;

For more information , follow this Perfect Full Page Background Image !!