Enable the Built-in PDF Reader in Firefox 15

" Mozilla recently rolled out Firefox 15, the latest version of the browser in their new rapid-release schedule.  With this new release there are quite a few new features, which have been outlined in the above linked post.  One interesting feature that bears a little more attention and some explanation is the new built-in PDF reader... "

Source: Ghacks.net
 Enable the Built-in PDF Reader in Firefox 15