As bssjersey points out, FF19 ignores your "Application preferences", described [ -US/kb/change-firefox-behavior-when-open-fi...] here and [ -US/kb/view-pdf-files-firefox-without-downl...] here as long as pdf.js is enabled. This is counter-intuitive and user-unfriendly. One shouldn't have to override settings (disable pdf.js) in about:config for an option configurable in the regular GUI to work as expected.