Question 1

Can we use firebase for highly scalable apps? Facebook, Instagram, etc like these?

Question 2

Yes.

Don't underestimate the amount of work it takes to build platforms of that scale on any technology however.

Manitej Pratha Sep 19 Developer @onecompiler · Accepted Answer

Can we use firebase for highly scalable apps? Facebook, Instagram, etc like these?

Yes.

Don't underestimate the amount of work it takes to build platforms of that scale on any technology however.

Firebase Team AMA