By default every internet address is on (all Firefox URLs whitelisted), and by default every email sender is on (all Thunderbird email addresses isn't blocked), to turn that around, to pick and choose URLs and email address correspondents, individually or with a list from a trusted source. (Or both.)
(Good one for our Dutch open source government and law enforcement:)
For your judgment. For my auntie, so to speak. (Though she didn't ask for it.)