Problem: Uploading a file from network share is blocking other requests

Paul Carson paul_m_carson at
Thu Jun 6 21:12:16 UTC 2013

I'm working on a RESTful web application.  This application allows the user to upload files to a server, which does some processing on those files and displays the results of that processing in a list.

Here's the problem:
One of the users of this application is running it in an isolated network.  All of the files they are uploading are located on a network share.  When this user uploads a file(s), Firefox is blocking all other requests (GET, POST, PUT, etc.) for the duration of the upload.  The requests are queued, but never sent to the server until the upload is finished.  At that point any queued calls that have not timed out, are sent.  This is a problem for them, because some of the files can be in excess of 2GB and take some time to upload, and they need to be able to access other portions of the application while the upload is in progress. This problem only occurs on that particular network, and only on FF. I've been unable to reproduce the issue anywhere else.  When testing, I often upload files from a network share and have never encountered this behavior.

Another interesting note: If the share is located on the client machine (i.e. \\localhost\share) the problem still occurs, but if I copy files from the share to the C drive on the client machine and do the upload with the local files, then FF behaves as expected.

As far as the application is concerned, there's nothing special about the file upload... it's just your basic multi-part form data POST using form.submit() (via YUI 2 library) in javascript.

The user is running FF 14.0.1, so I had them upgrade to the latest and the problem is still reproducible on FF 21.  Other browsers on their systems behave as expected.

Here's what I've tried:
Tweaking the max number of connections
Enabling/Disabling pipelining
Tweaking Proxy settings
I've looked briefly at the user's network configuration, and from what I can tell there's nothing amiss
I've looked at the windows event logs and they are clean
Googling the problem, but I haven't been able to find much :)

When looking through the FF bug lists I found this: which seems like it could be related, but I'm not positive.

I'm just looking for ideas here, anybody ever encountered something like this before? Any ideas where I should go from here?


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