Just tested with Norton Security with Backup and Mozilla Firefox 35.0.1. Loaded a website that Norton Safe Web considered bad (Warning rating). I was able to see the webpage for a split second before Norton IPS blocked Web Attack: Malicious File Download Request 27. Another second later or so and Norton showed the full page block ("Dangerous Website Blocked"). If I had Norton ConnectSafe configured, Norton IPS would have had nothing to do.