I have been using FF since it was almost of Beta. I never had had a virus on a PC I own/have ever owned. I watch You Tube videos, use FB and have never had an issue. I think all of it comes down to: "Should I have clicked that link?".
Ripley's picture on the Cookie Management is spot on. I did that a few years ago and I had to set aside some time to get things setup how I like it.