I think having ~/.mozilla/firefox/$foo.default/chrome/userContent.css containing

    @-moz-document url-prefix(http://news.ycombinator.com/) {
        td { color: #000000 !important; }
        a { color: #000055 !important; }
    }

helps an awful lot with news.yc's appearance. The main improvement being the banishing of that awful low-contrast gray on gray text.