In recent months I have found that I am unable to download or open PDF documents from web pages. Download links either open a blank page in a new tab or do nothing. PDFs that I am unable to view in Firefox can be viewed and/or downloaded in Safari most of the time and Chrome all of the time so I assume the problem is not my computer or operating system. I recently turned off the pop-up blocker but that did not make a difference. The problem has worsened over the past couple months, it appears that more and more web sites are moving to a different protocol for viewing/downloading PDFs. It used to happen occasionally but now I find that I am unable to view a majority - about 75% - of PDFs. I am using Firefox v18 for Mac with Mac OS X 10.6.8.