Safe? Don't put anything you don't want anybody to know about online. The way I see it, the people who are concerned about their privacy being breached, they are the ones doing it to their selves. People post everything in facebook, and then complain about their privacy? Now that's funny.
You are right about firewalls. Heck, I don't even have an anti-virus in my PC.
I have zero presence online. I don't have facebook or any of those social media apps. The only presence I have online, is the persona that I created specifically for internet usage. I am that paranoid, and it seems that my paranoia paid off with all these NSA spying issues.