How to allow keyboard focus of links in Firefox?

Ok, somebody explained this to me. It's a Mac problem. Mozilla is being true to operating system settings in Mac OS.

There are two distinct ways around this on the user side. Both seem to work:

1. In System Preferences → Keyboard, in the Shortcuts pane, check the “all controls” radio at the bottom.

2. In Firefox, type "about:config" in the URL bar. There is no accessibility.tabfocus preference on the mac, so you'll have to make one. Right click in the window, create a new "integer" pref, and set it to 7.

Neither of these are terribly obvious. Also, neither of these are a server-side solution for developers, which is frustrating.

On MacOS Big Sur this is done like this:

Tick the checkbox Use keyboard navigation...

I also didn't have to hack the about:config