Can you open the same pdf in the browser only? What OS? What version of Firefox? Did you clear your browser cache? https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox It appears that we will not be able to replicate your steps, so it will be up to you to troubleshoot this issue. Also try different version of Firefox(Beta, Dev, or Nightly) and see if you have the same issue. https://www.mozilla.org/en-US/firefox/channel/desktop/ Make sure to install in a different directory from the current install. Try turning off ETP to see if it makes a difference. see screenshot