Currently there is:
1. Left Mouse Button
2. Right Mouse Button
3. Cursor Left/Right
4. Mouse Wheel
5. Left button use in selection
6. Space key
The categories title is "Keyboard / Mouse", so I think Keyboard settings should be listed first and then Mouse settings.
A better order could be:
1. Cursor Left/Right
2. Space key
3. Left Mouse Button
4. Right Mouse Button
5. Mouse Wheel
6. Left Mouse Button in selection
Also the number of panels is a bit high and should be reduced.
#HM1 Current Dialog in 1.80 Alpha 1

#HM2 Proposal with order corrected and less panels

I think that #HM2 is clearer.
When drafting the dialog I've noticed that the "Middle Mouse button" is missing. Currently it will open the current image in fullscreen, perhaps also worth making it configurable. (Personally I do use the mouse wheel but never use the middle mouse button).
XnView 1.82 alpha