firefox下载文件名乱码（java）

if (request.getHeader("USER-AGENT").toLowerCase().contains("firefox")) {
    fileName = "=?UTF-8?B?" + (new String(Base64.encodeBase64(fileName.getBytes("UTF-8")))) + "?=";
} else {
    fileName = new String(fileName.getBytes("UTF-8"), "ISO-8859-1");
}
response.addHeader("Content-Disposition", "attachment;filename=" + fileName);