I have followed the directions to "activate" the native pdf viewer - but pdf documents only render part of the page or are entirely blank (when I zoom in and out, different portions of the page become visible but at no time is any one complete page visible). Using FF 44.0.2 on Macbook running OS X Mavericks; have tried disabling scripblockers and ad blockers. Also thought it might be related to mixed content blocking, so I tried to disable that, but there is no button that allows me to do so. (Followed the directions on the help site. Where the image on the help page has a "disable this for now" button, there is no such thing in my version of FF) I tried installing that other recommended viewer (named something like Schibert) - it's awful! Jerky navigation, ugly interface, laggy performance when trying to zoom, etc. NOT an acceptable option! The ONLY other thing that can be done is to just download every single pdf and open them on my computer. But often the pdf turns out not to be useful or what I thought it was, so then I have to go track it down and delete it; it was so much easier when I could just preview it in the browser and close the tab when I realized that it was useless to me. This is an enormous problem for me and has essentially rendered my favorite browser worthless for the tasks that I need to accomplish. It has only gotten worse with the last few "updates". At first, I could see pdfs on most sites, then it got progressively worse, so that now there is not a single site where I can access pdfs.