I don't understand what need is for CTRL/Command+R in the preview window. CTRL/CMD+F does the same IF cropping is selected. If you unmark the crop checkbox CTRL/CMD+F goes to full screen image but doesn't return from it if pressed again you have to use CTRL/CMD+R. But if you have cropping marked CTRL/CMD+F works both for full screen and for returning from it too. This makes me think CTRL/CMD+R is unnecessary and its current need (if unchecked) is even disturbing if you use any way of imput devices with preprogrammed shortcuts.