I think you’re missing a key area here. The original Mozilla product was Netscape- a commercial combined web browser and email client. There used to be a number of commercial competitors in the space, e.g. Opera, Eudora, etc. Microsoft killed that market in the 1990’s.
I struggle to see how any organisation could make money out of giving away a product that costs money to produce and promote. You’ve suggested they could have been Proton but that’s a completely different sector. We could just as easily have suggested they could have been Twitter, WhatsApp or Instagram.
What do you mean by external drive in this case? USB? NAS? What have you tried already?