If you are trying to make money and ship a product, then I have seen far worse than just a Front end and a Firebase. Go for it. Get your product in front of paying people as quickly as possible, then sell sell sell. You'll probably fail (the default state of a start up is failure), but you'll learn a lot along the way.
If your hope is to learn how to write code for other peoples products and have them pay you, it would benefit you to get a more full stack education. Node would be good. Rails is nice. Django is nice. .Net works well. Java is good.
It just depends on what your goals really are.