TypeError: Object(...) is not a function

Recent releases of AngularFire require rxjs 6. Please upgrade rxjs, you'll need to include rxjs-compat if you have dependencies that haven't yet upgraded.

Even though you can run rxjs-compat, its only a matter of time before you need to change your code to reflect the new RXJS. If you are using Angular 6 and the Angular 6 CLI, then you will have RXJS 6, since Angular depends on RXJS for most things. Also if you plan on using Angular Material 2, then you will need Angular 6. So lets just update your RXJS. This will be really important as of Ionic 4. Ionic 4 will depend highly on angular as it will now include the Angular Routes.

Some of the most common changes of RXJS 6 is:

import 'rxjs/add/observable/of';
// or 
import { of } from 'rxjs/observable/of';

Becomes

import { of } from 'rxjs';

and

import 'rxjs/add/operator/map';
import 'rxjs/add/operator/take';

becomes

import { map, take } from 'rxjs/operators';

and

import { Observable } from 'rxjs/Observable';
import { Subject } from 'rxjs/Subject';

becomes

import { Observable, Subject } from 'rxjs';

https://www.academind.com/learn/javascript/rxjs-6-what-changed/

This works for me, using "angularfire2": "^5.0.0-rc.11"

npm i rxjs@6 rxjs-compat@6 promise-polyfill --save

To retrieve the data:

this.db.list('/customers').valueChanges().subscribe((datas) => { 
  console.log("datas", datas)
},(err)=>{
   console.log("probleme : ", err)
});

Or you can check the GitHub repository for angularfire2 here for more details