When I'm introspective about the last few years I think the biggest mistake that we made, as a company, is betting too much on HTML5 as opposed to native... because it just wasn't there. And it's not that HTML5 is bad. I'm actually, on long-term, really excited about it. One of the things that's interesting is we actually have more people on a daily basis using mobile Web Facebook than we have using our iOS or Android apps combined. So mobile Web is a big thing for us.

We're a community of a billion-plus people, and the best-selling phones - apart from the iPhone - can sell 10, 20 million. If we did build a phone, we'd only reach 1 or 2 percent of our users. That doesn't do anything awesome for us. We wanted to turn as many phones as possible into 'Facebook phones.' That's what Facebook Home is.

We think the fact that Instagram is connected to other services beyond Facebook is an important part of the experience...This is an important milestone for Facebook because it's the first time we've ever acquired a product and company with so many users.

So I think that the scale of the systems has created this responsibility for us, where we have to be more proactive about finding and addressing issues [harmful content]. And we can do that both by building technology that is possible now, but wasn't even possible five or ten years ago, and by hiring people at a scale that would not have been possible for us before.

The world is changing so quickly, with mobile stuff and different platforms emerging, that I think it's more likely that the biggest competitor for Facebook is someone that we haven't heard of. What that means for us is that we should just really stay focused on what we're doing.

The main Facebook usage is so big. About 20 percent of the time people spend on their phone is on Facebook.