How to allow keyboard focus of links in Firefox?

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

Anyone looking at the second method explained within the accepted answer:

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.

Be aware that there is already a preference named accessibility.tabfocus within the Firefox Developer Edtion which is a boolean.

You can change this to an integer by clicking on the trash icon and deleting the preference. This will then allow you to select the type you would like the preference to be and allow you to assign it a value afterwards.

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.