For the past six months or more, when I download a file with Firefox, it will usually be corrupt. During those months, I've always kept Firefox up-to-date. I'm currently running 3.6.6 32-bit. Here are some details:

  1. If a download is corrupt and I immediately start the download again, and the source URL and destination path are identical, then the download finishes instantly and the file is then valid.
  2. It only happens for Firefox. I have no issues with IE, with any HTTP download managers, or downloads using any other transport protocol.
  3. It happens on more than one system, each system is completely different (one is hardware and one is a VM) and I run a totally different software firewall on each. They are both running Windows 7 64-bit, however.
  4. It happens even if I run Firefox in safe mode (no extensions or plugins).
  5. Regular web usage w/ Firefox seems to exhibit no problems. Web pages and images do not appear corrupt. However, downloads of extension updates sometimes fail their integrity checks.
  6. For what it's worth, anti-virus and malware scans come up clean and I take fairly strong measures to protect my browser and my system.
  7. It happens for both HTTP and HTTPS downloads.

I ran some tests downloading the same 2.5 MB .zip file 6 times in a row (renaming the source file each time so it wouldn't cause #1 above to trigger) and compared the corrupt files with a valid file in WinMerge. Each time, the corruption is different. Most of the file contents match, with segments always missing from the corrupt file. In one of the six cases, however, a segment of file that shouldn't exist was inserted into the corrupt file, as well. The chunks of corruption, whether missing, erroneous, or added, appear in WinMerge to be similarly sized, perhaps related to Firefox's download block size?

While a number of things could explain some of the symptoms, I cannot determine a cause that would fit them all, particularly #3. Any help would be greatly appreciated.

  • Install Firefox 4 Beta 1 and try again.
    – Hello71
    Jul 11 '10 at 0:22
  • I tried Portable Firefox 4 Beta 1, and it did not help, unfortunately.
    – Gregyski
    Jul 17 '10 at 19:40

Uninstalling and re-installing firefox should do the trick.


I've got the answer, works for me. advice from my friends.

  1. Click Start and open the Control Panel
  2. Choose Network and internet.
  3. Open the Internet Options applet
  4. Click the Advanced tab
  5. Scroll down to and uncheck the box next to Use HTTP 1.1
  6. Clik ok.

Once this is done, open firefox and try downloading the Zip file again.


Well, here are two thoughts:

Firstly, I've noticed that when this happens to me, it's usually related to my Internet connection. Specifically, it seems to happen a lot at work where certain ports and sites are blocked. Is it possible that you are in the same situation? I notice that I'll start a download, but that the download may be cut off mid-stream by Big Brother (thus becoming corrupt).

Secondly, have you tried all the steps here ?

It may not be likely that these steps will help, but it'll be good to be able to say that you've covered all the obvious bases. Good luck!

  • On the first point, that's definitely not what is happening. These files are not being truncated, but rather have segments missing, corrupted or added in various parts of the file (usually the middle). On the second point, I don't see much in there that applies directly, but a few of them appear to be at least worthwhile to try. Thanks for the suggestions, I'll report back once I've tried those steps that have any potential.
    – Gregyski
    Jul 11 '10 at 15:48
  • Is it a problem with Firefox specifically? In other words, are other browsers able to successfully complete the same download?
    – jrc03c
    Jul 11 '10 at 16:12
  • Yes, Firefox specifically. Please see #2 in my question.
    – Gregyski
    Jul 11 '10 at 16:59
  • Ah, yes. Sorry.
    – jrc03c
    Jul 12 '10 at 13:40
  • Did you try re-installing Firefox?
    – jrc03c
    Jul 12 '10 at 16:53

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