Browsing delays after enabling FSSO

Hello,

We are doing FSSO based user authentication (with collector agent) in firewall policies with FQDN based web filtering (transparent proxy). After enabling FSSO, we noticed a significant increase in delay at web browsing. I'm not sure if this is due to the FSSO authentication process, the DNS (since we do FQDN filtering) or something else. Has anybody experienced similar behavior in web browsing with FSSO enabled? Any suggestions?

Thanks