Bug 1503537 - Get rid of the pdfium & mortar code r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D10352

browser/app/profile/firefox.js

@@ -1298,11 +1298,6 @@ pref("toolkit.startup.max_resumed_crashes", 3);
 pref("toolkit.winRegisterApplicationRestart", true);
 #endif
 
-// Whether we use pdfium to view content with the pdf mime type.
-// Note: if the pref is set to false while Firefox is open, it won't
-// take effect until there are no open pdfium tabs.
-pref("pdfium.enabled", false);
-
 // Completely disable pdf.js as an option to preview pdfs within firefox.
 // Note: if this is not disabled it does not necessarily mean pdf.js is the pdf
 // handler just that it is an option.