I've just turned my website into a responsive layout and along the way I've somehow managed to make my dropdown menus not work. When hovering over 'Drop-downs' they don't display unless I'm using position: relative. They worked before using position: absolute - but it seems they only work with position relative now. When using relative it uses the width which messes up the navigation bar.

Using relative: http://d.pr/i/tp5R
Using absolute: http://d.pr/i/j7r1

CSS for my sub-menu

div.left_first_header ul.sub-menu {
    width: 125px;
    top: 14px;
    z-index: 2;
    height: 100%;
    position: absolute;
    -webkit-border-radius: 0px 0px 4px 4px;
    -moz-border-radius: 0px 0px 4px 4px;
    background: url(images/drop_down_bg.jpg);
    padding-left: 15px;
    padding-right: 15px;
    background-repeat: repeat;
}

jQuery for the drop down functionality

jQuery(document).ready(function ($) {
    jQuery("ul.dropdown li").hover(function() {
        $('ul:first',this).css('visibility', 'visible');
    }, function() {
        jQuery(this).removeClass("hover");
        jQuery('ul:first',this).css('visibility', 'hidden');
    });
});

My website
http://wpvault.com/kahlam/

Considering it's 4am I've probably made a really stupid simple mistake.

I apologise if I've missed anything.