Steps to reproduce:

• create a pixiv account
• go to https://www.pixiv.net/en/artworks/99827898
• click on the main image to load the full-resolution version
• drag the main image to the nemo file manager

Under i3wm (x11) the file will be saved successfully. Under sway (wayland) the file manager is stuck attempting to copy the image.

I suspect the difference is that under X11 firefox attaches the file contents, image file path in the disk cache, a file descriptor or something like that to the drag event while under wayland it only sends the URL which can't be downloaded because it requires a login.

Compositor: Sway 1.8

Name Firefox
Version 110.0a1
Build ID 20230106214742
Window Protocol wayland

Can you try mutter compositor?
https://fedoraproject.org/wiki/How_to_debug_Firefox_problems#Testing_different_Wayland_compositor
Thanks.

The issue also occurs in mutter.