I didn't have to change anything in macOS settings but only in Firefox.
The TL;DR is roughly this:
about:configin the address bar.
accessibility.tabfocusin the input field to search for that property.
Numberand value =
Now you should be able to tab through all tabbable elements on a page.
The other day I was trying to run an accessibility audit with Firefox on macOS when I realised that I was not getting some focus styles in certain elements that should be tabbable.
I went and tried with another browser, Chrome and it turned out that everything worked as expected. However, since I want to support Mozilla <3 I wanted to make it work for Firefox too.
I remembered that long ago I had a similar problem and enabling some setting in the preferences page did the trick, sadly this was not the case anymore and I couldn't find that magic checkbox anymore.