Default download dialog is visible in some cases

[Lekensteyn]

In some occassions, I have noticed that the open-in-browser download dialog window is being opened (but not rendered) and then quickly closed and replaced by the default dialog. So far I have only observed it with two HTTPS sites, any attempt to reproduce it locally with plain HTTP does not have any effect. It is also not 100% reproducible, there are rare cases where the download dialog is shown (maybe a race condition based on network quality?)

One failing example that I have been reproducing with is the "Download PDF Format" on the https://oyster.tfl.gov.uk/oyster/journeyHistory.do.

In a failing case, the onErrorOccured callback is invoked with NS_ERROR_NET_ON_RECEIVING_FROM. In Wireshark, I can observe that the server sends a TCP FIN/ACK right after sending the data and receiving an ACK from the client. The client then sends a close_notify TLS alert and also closes the connection.

Due to triggering this abortionObserver signal, the ModalDialog is immediately closed.

[Lekensteyn]

Reproducer:

openssl req -newkey rsa:2048 -x509 -nodes -keyout server.pem -new -out server.pem -subj /CN=localhost
python repro.py

Visit https://localhost:4433/, accept the certificate. The faulty behavior will become visible.

repro.py:

from socketserver import TCPServer, BaseRequestHandler
import ssl
import time

#body = open('foo.pdf', 'rb').read()
body = b'x' * 13230
head = b'''HTTP/1.1 200 OK
Content-Type: application/pdf
Content-Disposition: attachment; filename="foo.pdf"
Content-Length: %d
Connection: close

''' % len(body)

PORT = 4433
class Handler(BaseRequestHandler):
    def setup(self):
        self.raw_sock = self.request
        self.request = ssl.wrap_socket(self.request, certfile='server.pem',
                server_side=True)

    def handle(self):
        sock = self.request
        sock.recv()
        response = head.replace(b'\n', b'\r\n') + body
        size = 1024
        while response:
            chunk, response = response[:size], response[size:]
            self.request.write(chunk)
            time.sleep(.01)

    def finish(self):
        self.raw_sock.close()

with TCPServer(("", PORT), Handler) as svr:
    svr.serve_forever()

[Rob--W]

Can't reproduce in a fresh profile on Firefox 57, Firefox Nightly (59.0a1).

Did you install any other add-ons or software that may interfere with the request handing of Firefox?

[Lekensteyn]

nope, it was a clean profile. reproduced with the version from AMO and also the one from #27.

Maybe try to keep dev tools open on the network tab?

[Rob--W]

Opening the devtools is necessary to reproduce the bug.

I reported this bug as https://bugzilla.mozilla.org/show_bug.cgi?id=1420917