Was there another API change recently? I had to revert to version 0.9.0 of Kodi add-on Moebooru, as the API now returns full URLs (including "http:") again. Indeed, it's author isn't even aware.

For Kodi users with Moebooru installed (if any remain, looks like I'm the only existing one) and not working anymore (thumbnails and pictures not showing), revert to version 0.9.0 and disable auto-update in the add-on settings.