userChrome.css to work around Firefox bug

userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
@namespace html url("http://www.w3.org/1999/xhtml");

@-moz-document url("chrome://browser/content/browser.xul") {
    button .button-text {
        color: black;
    }
}

@-moz-document url("chrome://global/content/commonDialog.xul") {
    button .button-text {
        color: black;
    }
}