Shortened footnotes are a mix of standard footnotes and parenthetical referencing (Harvard). They use in-text citations that link to a shortened reference in a list and a separate full reference list. The shortened reference may link to the full reference.
Shortened footnotes are used for more reasons: they let the editor to cite many different pages of the same source without having to copy the entire citation; they avoid the inevitable clutter when citations are inserted into the source text.