Firefox about:config settings:

browser.download.improvements_to_download_panel		;false
browser.newtabpage.enabled				;false
browser.pocket.enabled					;false
browser.privatebrowsing.autostart			;false
browser.safebrowsing.downloads.enabled			;false
browser.safebrowsing.downloads.remote.enabled		;false
browser.safebrowsing.enabled				;false
browser.safebrowsing.malware.enabled			;false
browser.tabs.animate					;false
browser.tabs.warnOnClose				;false
browser.urlbar.autocomplete.enabled			;false
browser.urlbar.suggest.bookmark				;false
browser.urlbar.suggest.history				;false
browser.urlbar.suggest.openpage				;false
browser.urlbar.trimURLs					;false
geo.enabled						;false
network.dns.disablePrefetch				;true
network.http.referer.XOriginPolicy			;1
network.prefetch-next					;false
network.trr.mode					;0
places.history.enabled					;false
reader.parse-on-load.enabled				;false
security.dialog_enable_delay				;300
widget.gtk.overlay-scrollbars.enabled			;false
widget.non-native-theme.gtk.scrollbar.thumb-size	;5