Remote debugging over USB with Android Phone is stuck in "Waiting for browser..."

Question

I am following the guide provided by MDN to remotely debug. I have made sure that I allowed USB Debugging on my Android phone. The version of my PC's Firefox is 72.0.1 and the version of my phone's is 68.4.1.

I've done the instructions below:

Enable Developer settings on your Android device.
Enable USB debugging in the Android Developer settings.
Enable Remote Debugging via USB in the Advanced Settings in Firefox on the Android device.
Connect the Android device to your computer using a USB cable.

My device has been correctly detected. However, it's stuck in "Waiting for browser..." I have opened a new tab, which I want to debug, on my phone's Firefox. How do I fix that problem?

For reference, here's the picture of "Waiting for browser...":

EDIT

It turns out that I forgot to enable Remote debugging via USB in Firefox on the Android device.