You can either set a static width to the site or you will have to play around with the CSS for the search, rss, and comments icons and fields. You have several absolutely positioned items which can be tricky work with. This won't fix your problem but if you add the following to ATO>Add HTML/CSS Inserts>CSS Inserts the header won't jut out when resizing but the icons are now not positioned correctly but maybe it will point you in the right direction.
HTML Code:
td.feed-icons {
position: absolute;
}