Looking at latest beta, I'm reminded that the auto image size functions in browser and viewer/options are completely unrelated. While I think this can be useful, having identical names attached to different functions is puzzling.
In browser, a naming alteration could have less mystery.
Auto image size > Auto preview size
with sub-items as:
Fit image to window > Fit preview to window.
Distinguishing auto image sizes
Moderators: helmut, XnTriq, xnview