The project is called pdf.js and is available for everyone to see on GitHub. It has been in development for about a month now, but there's already an early demo available at people.mozilla.org/~gal/test.html that you can check out for yourself. There are still glitches and rendering artifacts, but it's definitely a good start, especially for four weeks of work.
The first order of business is to get pdf.js to render PDFs "natively" in Firefox itself, and the team believes it can get the most commonly used PDF features working in less than three months. The group will start by making a Firefox extension available to interested users that enables inline PDF rendering using pdf.js.
The next step will be to ship pdf.js with Firefox. The team hopes this will result in a substantial usability and security improvement for Mozilla's users since pdf.js uses only safe web languages and doesn't contain any native code pieces attackers could exploit.
Last but not least, pdf.js will hopefully turn into a community driven and governed open-source project. It will be used in Firefox, but hopefully it will also be ported to other browser and opened up for use in other applications. The project pdf.js is being licensed under a very liberal 3-clause BSD license and external contributors are welcome to join.
"It's important to note that we're not trying to promote PDF to a first-class web citizen like HTML5 is," Andreas Gal writes in a statement. "Instead we hope that a browser-native PDF renderer written on the web platform allows web technologies to subsume PDF."