To select files for upload, I like to drag files from nautilus (file manager) onto the corresponding file selection button on websites. This usually works fine, but today (after doing it a few times already), it suddenly stopped working.
What happens in the error case is that instead of accepting the file, an entirely unrelated URL is opened by Epiphany. I have seen this happening before. Unfortunately I have no idea how to reproduce this issue and I didn't see anything relevant in the logs.