Hallo,
what about the addtion of the Apple+"+" and “-” command within the preview window?
I think it is missing in the contextual menu.
“Right-click” mouse button, wait until menu pops up, choosing “greater” or “smaller” with mouse-pointer is IMHO far to slow 
It should be easy to do, isnt it?
Kind regards
Those shortcuts are already used to increase/decrease the font size of the selected text, see menu Format. To zoom in/out, use Cmd-Ctrl-Up/Down Arrow, see menu View.
Yes, indeed…sorry.
I have tried the standard commands and did not look in the menu.
But could it be possible to integrate an CMD+“scroll button” for resizing, as integrated in Firefox?