We just got Firefox 18 earlier this week, but Mozilla already has its sights set on the future. That future is one devoid of PDF plugins, like Adobe Acrobat Reader, that could harbor dangerous security flaws. Instead, the non-profit will continue pushing HTML5 in the new year.
For a number of years there have been several plugins for viewing PDF’s within Firefox. Many of these plugins come with proprietary closed source code that could potentially expose users to security vulnerabilities. PDF viewing plugins also come with extra code to do many things that Firefox already does well with no proprietary code, such as drawing images and text. These problems, and the desire to push the boundaries of the HTML5 platform, led Andreas Gal and Chris Jones to start a research project they named PDF.js. The project quickly picked up steam within Mozilla Labs, where it grew into a full-fledged PDF viewer.
PDJ.js is now available in Firefox 19, but it's still in beta so bugs may be present. To that end, Mozilla encourages beta users to file bug reports if they run into any problems. The developers want to get PDF.js into the release version of Firefox, and plenty of bug reports will help them polish it up for release six weeks from now.
As for developers, you can help contribute to the project by visiting the PDF.js github page. It would be an excellent opportunity to work in more advanced HTML5 projects.