Facebook does track browsing activity. It does so through the like button on outside websites and the Facebook Pixel. Zuckerberg appears unwilling to say this.
Okay, I'll answer some of the questions, using Facebook's website!
Does Facebook track you off Facebook? Yes, via the Facebook Pixel: "A piece of code for your website that lets you measure, optimize and build audiences for your ad campaigns." facebook.com/business/help/… 
Can Facebook track you offline? Via Offline Conversions, it works with businesses you visit (they provide the data) to figure out if you saw a Facebook ad before your visit: facebook.com/business/help/…
And then there's the Like button on websites around the web: "If you’re logged into Facebook and visit a website with the Like button, your browser sends us information about your visit."
So yeah, easy answers here. It's all on the website.
Ah, and here's the answer to "logged out" tracking! It's yes. "If you’re logged out or don’t have a Facebook account and visit a website with the Like button or another social plugin, your browser sends us a more limited set of info." facebook.com/help/186325668…
Zuckerberg can't say how many webpages have the data-tracking Facebook Like button, Facebook Share button, and Facebook Pixel
Okay, got some more detail and links to everything on Facebook's website about how it tracks you when you're not using it:
Here's How Facebook Tracks You When You're Not On Facebook
buzzfeed.com/alexkantrowitz…
Here's How Facebook Tracks You When You're Not On Facebook
buzzfeed.com/alexkantrowitz…
