Firebase was acquired by Google some few years back. Angular is a frontend framework by Google. Firebase is a platform, not a frontend framework like Angular.
You can use Angular/React/VueJS/Ember/etc... with Firebase, these are all frontend frameworks.
Firebase is like a different kind of Backend-as-a-Service (BaaS). Graphcool is also another kind of BaaS. But Graphcool is more powerful, as it has more expression to the data, and doesn’t get your get confused in all steps of the way.
In my opinion, Firebase is also an interesting platform. It’s just that only a very few usecase makes sense for it, namely simple usecases; anything data intensive, and you’ll deal with an endless line of rules. Graphcool, on the other hand, can be used for even your most data complex usecases.