Well I need my Firebase access for sure, and I tried installing the fcm-plugin, but this raised even more compatibility issues. I am pretty sure by now tho, that this can entirely be solved by the firebase.message() feature, since installing fcm and push results in a lot of problems. I will look into this in more detail tomorrow. For now I suppose I plan on working without the push plugin.
Here I found some related problems to mine. But I will for sure tell you, when I got anything to work 