By "keyboard" I assume you mean TAB-key-based navigation (I don't know of any other included in the browsers)? If so, it looks to me that links are in fact TAB-stops, but they're not being highlighted. It's something that should be solvable with a CSS adjustment.
If the links are not highlighted by default, then tab navigation is basically non-existent since I cannot see where I'd be redirected and I personally bother to write custom CSS only for the websites I visit very often.
Is there an actual reason to disable highlighting? It lowers usability and accessibility, but I'm not sure what do you get in return?
