Step 1: Describe your environment

• Operating system: _____Window
• Browser: _____Chrome
• Firebase SDK version: _____9.14.0

Step 2: Describe the problem:

Steps to reproduce:

1. _____I don't know why, but when it's in the background it shows two messages

2. ---

3. ---

Observed Results:

• What happened? This could be a description, logs, etc.

Expected Results:

• What did you expect to happen?

Relevant Code:

// TODO(you): code here to reproduce the problem
I have made no changes, only the example code