Don't use pref 'browser.download.improvements_to_download_panel' in Firefox (#14822)
Don't use pref 'browser.download.improvements_to_download_panel' in Firefox (#14822)

showpad/mozilla-pdf.js,showpad/mozilla-pdf.js,mozilla/pdf.js,timvandermeij/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,mozilla/pdf.js,mozilla/pdf.js,Shoobx/pdf.js,Snuffleupagus/pdf.js,Shoobx/pdf.js,nawawi/pdf.js,timvandermeij/pdf.js,nawawi/pdf.js,timvandermeij/pdf.js