XnView Software

In Settings-General-File Operations, there is a "Confirm file delete" option.
This is great
…but it would be nice with "Confirm file/folder copy" and "Confirm file/folder move" options as well. (I recently accidentally copied some folders. Granted, my mouse does misbehave a bit, occasionally [should replace it], but still…)
(Actually, I'd love having all actions that make any file/folder changes, require a confirmation, but… especially ones that are easy to do by accident)

when you drag&drop a folder from thumbnail view into folder tree view?

No. When I accidentally drag&drop within the folder tree. It is a rather difficult thing to do, between the views.