In Photo Grid and Square Grid, Home and End make the first or last photo of
the view the active, selected one, and Shift+Left / Shift+Right add the
previous or next photo of the view to the selection. These keys wait while
the full-screen preview covers the grid, in every other view, while a text
field or a dialog has the keyboard, and when the user gave the key to a
command. They are listed under Fixed keys in the keyboard shortcuts dialog.
Open Library now has Cmd+O and Visualize HDR has Shift+H (Cmd+Shift+H stays
the Histogram).