He's using 'su' to switch to desktopuser, that's not necessarily, and quite likely not, an account with root privileges. 'su' stands for 'switch user', it's not just to become root.

Correct.

I use a script in a root terminal to control a lot of my workflow. One thing is that I start browser windows from it when needed. I start them with

    sudo -u desktopuser chromium example.com

Because

    sudo -u desktopuser firefox example.com

does not work.

I thought that is relevant to the question "Why bother with Chrome".

desktopuser of course is the normal user which would also start Firefox if I did it via the Desktop gui.

He uses the term “root terminal”, he writes “Start a root terminal (or a normal one and then ‘sudo su’)”, and he says he only has a single user. One will naturally assume the worst, and in spite of repeatedly posting here he hasn’t exactly made much sense about his workflow and needs beyond launching the browser.

You're right, I missed the root terminal part.