Sorry for the late response.
First, add this to your css:
.ngg-gallery {
width: 100% !important;
max-width: 350px; /*here you want to enter the maximum width of your slideshow */
}
.ngg-gallery img {
max-width: 100% !important;
height: auto !important;
}Then, add this Javascript:
<script type="text/javascript">
jQuery( window ).resize(function() {
var cw = jQuery('.ngg-slideshow').width();
jQuery('.ngg-slideshow').css({'height':cw+'px'});
});
</script>This should work. More information can be found here: http://wordpress.org/support/topic/plugin-nextgen-gallery-how-to-make-gallery-responsive-to-browser-size?replies=30