Steps to reproduce:

1. Pick a large file to upload (9-10MB seems to do the trick)
2. Remove the file ASAP, before it's done uploading
3. The console will output "Retry #1 on error event"
4. Subsequently the upload will be silently retried twice. It shouldn't retry at all, since we've consciously removed the file.

Note that it doesn't seem to happen every time, it seems to be subject to a race condition, but it's easy enough to reproduce locally on Firefox if you try a few times.