Which font(s) does Google Chrome use by default?

When designing websites, I've noticed that Chrome and Firefox have different default fonts, or at least, they look different somehow. Rather than serving fonts to all users, I think what I'd like to do is just use Chrome's default font, and serve that to Firefox users. What font(s) does Google Chrome use by default when websites don't specify a font?

Also, apologies if this question doesn't fit here, I wasn't quite sure if UX includes UI development.