The browser maker described the built-in PDF viewer as more secure and safer than proprietary PDF viewing plug-ins, like those installed by Adobe Reader or Foxit Reader. However, several security experts noted that it probably won't be free of vulnerabilities.
"For a number of years there have been several plugins for viewing PDFs within Firefox," Mozilla Engineering Manager Bill Walker and Mozilla Software Engineer Brendan Dahl said Friday in a blog post. "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."