Changes the new Stack Exchange top bar so that it stays fixed even when scrolling.

Fix SE top bar to window top

@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain('stackoverflow.com'),
domain('stackexchange.com'),
domain('superuser.com'),
domain('serverfault.com'),
domain('stackapps.com'),
domain('askubuntu.com'),
domain('mathoverflow.com'),
domain('answers.onstartups.com'),
domain('mathoverflow.net') {

    header.top-bar {
        position: fixed;
        top : 0;
        z-index: 1001; /* move in front of stuff */
        width : 100% !important;
    }

    /* Moves the sidebar on "Ask question" so it does not become partially hidden. */
    div#scroller {
        transform: translateY(34px) !important;
    }
    div.ask-sidebar {
        overflow : visible !important;
    }
    
    /* Moves the review bar so it does not become partially hidden. */
    div.review-bar {
        top: 34px !important;
    }

    /* Makes dismissable headers visible again. */
    div#overlay-header {
        z-index : 1002 !important;
    }
}

Adapted from Rob W's version using another comment of his.