I really like Fire­fox 3 and have always used it as my default web browser on both the Mac and PC plat­form. How­ever, the way that Fire­fox han­dles PDF files is some what of an annoy­ance. If you are like me you too will find it rather odd then that when in Fire­fox and you click on a web link to a PDF file it will auto­mat­i­cally down­load the file and then open the PDF up in Apple’s default Preview.app. Now the eas­i­est way to solve this prob­lem is the go ahead and start using Safari. How­ever, one of the rea­son I use Fire­fox is for the amount of add-ons, exten­sions and cus­tomiza­tion you can do in it. So as usual their is a Fire­fox exten­sion which adds this fea­ture. (I believe their is an exten­sion for pretty much every­thing) This sim­ple exten­sion adds the abil­ity to view PDFs directly into Fire­fox. You can down­load the Fire­fox exten­sion here.