I only report it now because I noticed this recently, but I don't think
I had the issue in last may.

On one of the sites I have to use professionally, after a file was
uploaded and I disconnect from the site and close the tab, lsof shows
the file handle is still used by firefox ; and if the file is on an usb
key, I have to force the ejection as it means it's seen as busy (which
is how I detected the issue).

Cheers,

J.Puydt