That's right no separate Adobe plugin and no Google secret-sauce non-open stuff either.
Well eventually it will work...currently the project is at its 0.2 release and it's still not quite ready for prime time. As it turns out there is a whole lot of complexity in dealing with different operating systems when it comes to rendering fonts for PDF.
"pdf.js produces different results on pretty much every element in the browser×OS matrix," pdf.js developers wrote in a blog post. "We said above that pdf.js renders the Tracemonkey paper “perfectly” … if you’re running a Firefox nightly. On a Windows 7 machine where Firefox can use Direct2D and DirectWrite. If you ignore what appears to be a bug in DirectWrite’s font hinting."
The day will come, thanks to the work of Mozilla developers when PDF will just be, yet another element that a browser handles as part of its core functionality. That's a good thing.