mre: XHR'ed dataTransfer file-descriptors remain open

dragdrop a single file onto this website;
an XMLHttpRequest will PUT the first byte to /

firefox does not close the file-descriptor until the next gc(?)
after the upload has completed, even if the tab is closed.
This can take anywhere from 15 seconds to never.
Problematic if the file resides on a usb flashdrive, making it
impossible to immediately safe-remove it, unless you perform a
manual gc in about:memory or close the browser

on macos, the file-descriptor seems to never be closed at all

on linux, the file-descriptor is usually closed after ~30sec,
     however in some cases it never gets closed / freed at all

screenshot: https://ocv.me/stuff/bugs/firefox/fd-delayed-close.png

reliably reproduced on:
  105.0.1 linux64 (mozilla-official build on debian-11)
  105.0.1 macos

NOT reproduced on:
  105.0.1 win64 on windows10