This is excellent for security. In the same way that Mozilla's PDF.js does PDF rendering in-browser and in-sandbox, doing SWF rendering in-browser and in-sandbox makes the security nightmare that is Flash go away.
ADDED: Mozilla blogging about security benefits of PDF.js, which apply here too to
ADDED: Mozilla blogging about security benefits of PDF.js, which apply here too to
http://andreasgal.com/2011/06/15/pdf-js/