You need to unclutch and stop worrying. Do the Mooladhara Dukha Harana Meditation.
<%
String userAgent = request.getHeader( "User-Agent" );
boolean isFirefox = ( userAgent != null && userAgent.indexOf( "Firefox/" ) != -1 );
response.setHeader( "Vary", "User-Agent" );
%>
k thnx