Does that really matter?
In Firefox and IE there is a focus border anyway. IE doesn't support :focus or outlines, so there isn't much you can help. In Firefox Cursor-Mode (F7) uses small text-cursor that isn't good for bad sighted people anyway. Opera with spatial navigation always adds background on focused links.
I don't know how mac browsers deal with this though.
-- regards, Kornel Lesiński
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