Both of them are well diversified and have solid market share in their areas. Apple is a juggernaut with the highest margins on smartphones in the industry, by far. Amazon now has 60%+ of online retail and is very profitable with its web services (AWS).
I think Google is solid for a while.
Facebook and Netflix are very vulnerable. Facebook is no longer "cool" and quickly being known as the "old ladies with cat pictures" site. Netflix has a lot of competition in their space including YouTube, which is basically free if you can stand a commercial or two. Both these companies could go the way of MySpace and Blockbuster in the blink of an eye.
Regarding NetFlix........ There is a war in process as the cable industry spoils are being gobbled up. Every body and their brother is attempting to move to the internet. Fox News is now in the process. Everyway of monetizing the move is being tried.
I liken it to the old days when there were tons of computer manufacturers and you argued with your friends over which was best.
Netflix has lots of customers for what is without doubt the best device. There is an attempt to vastly broaden the customer base by taking on international programming and customers.
I think there will be many that die by the wayside before NetFlix is gone
You do know that Google (parent Alphabet) owns YouTube, right?