This code is highly inspired by a stack overflow answer.

A default, internal configuration defines my preferred browser (firefox) as the default, but then places at least one link to Google Chrome - meet.google.com.

You can update the config file - /etc/usbrowser_config.yml to make system-wide changes, and/or create a config file for your user called ~/.usbrowser_config.yml.

There is a sample file in /usr/share/usbrowser/examples/usbrowser_config.yml.