Using Image mode was a workaround for the problem of losing double-tap-to-return-to-thumbnail-mode
functionality (described here
). Image mode helped by exposing the "x" button to close the app.
But since that problem has now been resolved, this workaround is no longer necessary.
So now it's just a matter of double-tapping to toggle between thumbnail mode to browse and fullscreen to view .. in all contexts: whether XnView was launched directly or whether it was launched by association with a file extension.
Which all now means the urgency of honouring gestures in Image Mode is no longer there.