horizontal scroll breaks with overflow-x:hidden in safari and firefox

[admin]

I have horizontal scroll on a wordpress site which works in chrome on all computer but not in some computers on safari and firefox.

My code is:

html {
    height:100%;
    overflow-x:hidden;

}
body {
    width:3080px;
    overflow-y:hidden;
}

when i remove overflow-x:hidden; the horizontal scroll works but you can see the scrollbar.
here is a link to the site <a href="http://happybirthday.irinanisimova.com/photography/" rel="nofollow">http://happybirthday.irinanisimova.com/photography/</a>

How can I hide the scrollbar? Also do you know why this works on some computers in safari and firefox but not all?

Thanks!