When the built-in PDF viewer was introduced at FF 19, I found that certain PDFs would not open in the browser ... due to this, I directed all of my end users to use the Adobe Acrobat plugin. Since at FF 52 the Adobe Acrobat plugin is no longer a viable option, I decided to try out the built-in viewer once again. It appears a lot of the problems I noticed back in 19 are gone; however for larger PDFs (e.g., http://www.tigardmaps.com/MapGalleryPDFs/b_admin_bndry/a_City_bndry/cty_bndry3444.pdf) I'm finding that the built-in viewer takes over 2 minutes to load the document whereas Internet Explorer and Chrome both took around 11 seconds. I've decided to peg my end users at FF 51 for now so that they can still use the Adobe Acrobat plugin. Is there anything that can be done on my end or in Firefox to address the really slow loading times for large PDFs? Thanks!