Apple icon -> System Preferences -> Keyboard -> Shortcuts -> checkbox for "Use keyboard navigation to move focus between controls"
I found this setting while googling last week after getting frustrated that Firefox wasn't letting me tab to links as I expected when it worked just fine in Chrome.
Interesting. How do I first get focus on the menu bar without clicking with the mouse?
Honestly, I have no idea. I did not know about your suggestion, so that's a TIL for me, but if I am going to click to get to the menu bar, it's not much of a solution.
(In Safari, tab takes me around the page. In terminal, it does what I expect, command/line completion. Only after I click on a menu does it get me anywhere. And it's a good the arrow keys do the same thing, because once one gets to Help, tab is stuck in the search field.)
I found this setting while googling last week after getting frustrated that Firefox wasn't letting me tab to links as I expected when it worked just fine in Chrome.