I can't speak to Facebook's intentions or policys(I don't use big blue app at all), but many sites use tools like Full story to discover bugs or watch a customers user journey to discover flows that aren't working well. Some portions of the page are automatically filtered(inputs with type=password), and the rest depends on the team being very thoughtful about marking sensitive portions of the screen as such.

It's a very manual process, but probably one of the most powerful tools for improving user experience I've ever seen. And typically for most businesses, you are keeping these sessions for 2 weeks or thirty days at most.