Firebase storage slow when delivering public images

Firebase storage slow when delivering public images

I'm using firebase storage to upload avatars (original.jpg).
In a node.js background process I resize them with gm and then put them back in my firebase bucket. These pictures are publicly readable, see my storage rules :
service firebase.storage {
  match /b/xxx.appspot.com/o {
    match /images {
      match /{allImages=**} {
        allow read;
      }
      match /{userId}/avatar/original.jpg {
        allow write: if request.auth.uid == userId;
      }
    }
  }
}

I store the url of images in firebase database ex: 
https://firebasestorage.googleapis.com/v0/b/xxx.appspot.com/o/images%2Fyyy%2Favatar%2Fzzz-small.jpg?alt=media

That I retrieved right after the file upload (web sdk) var downloadURL = uploadTask.snapshot.downloadURL; ; stripped off the token parameter as it's gonna be public ; and where zzz-small.jpg has replaced original.jpg.
It works, pictures are displayed.
But it's slow even though the picture is a 40x40px jpg. And it hangs for a while before actually downloading the file, see Chrome Network record :
Chrome network record
The file is 158B, there's a ~1s waiting before the download ~3ms...
Is firebase storage supposed to be as fast as a CDN ?
Any faster way to call a public readable file ?
[EDIT]
Got some feedback from Firebase support :

We're definitely aware that many users, such as yourself, are having
  issues with slow downloading of file from Europe. We're exploring
  potential solutions, but I can't share any details or timelines at
  this time. We'll keep your feedback in consideration moving forward
  though.
Keep an eye out on our release notes for any further updates.

I forgot to mention I'm in Europe and the storage in the US.

Solutions/Answers:

References

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