The keyboard shortcut [Ctrl+X] for the command "cut image" does not work initially. The command "Cut" has to be selected from the Edit menu once to enable the shortcut. After exiting from full screen or the viewer back to the browser, the shortcut is disabled again.
EDIT: Never mind, I just learned this issue is already fixed in the next release v0.80.
[v0.79]: Broken keyboard shortcut [Ctrl+X]
Moderators: helmut, XnTriq, xnview, Dreamer