Files downloaded with Firefox are often corrupt

Question

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.

Answer 1

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:

http://kb.mozillazine.org/Unable_to_save_or_download_files

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!

Answer 2

I've been experiencing the same corruption of download files (zip/tar.gz) using FireFox 5.0 and downitall plugin. I don't experience the issue using the nighly build of Firefox 6.01a with downitall plugin.

Answer 3

I had the exact same problem. I found that uninstalling and then reinstalling FireFox made it work.

Answer 4

I have a similar problem with Firefox. I used Firefox for a long while without any problems and I don't exactly remember what version of Firefox I updated. I guess it was Version 5 or 6. After this update to the newer version I immediatly noticed that the size of exactly same downloaded files differs if I downloaded the file again. I deactivated all addons, plugins and run Firefox in safe mode... without any success. The files differ in a random manner. If I used IE or a download manager, the file sizes are always equal. Only if I use Firefox the filesizes always differ.

First I analysed the files that I downloaded with firefox: whatever file I download, all files are messed up with zero-Bytes always at different positions. In the most cases the zero-Bytes are attached at the end of the file.

Second I tried Firefox in the same Version on other Platforms with Win2000, WinXP and OpenSuse. There I can't adjust the Problem, all downloaded files had the same correct size. Next I tried to download the file locally on the desktop instead downloading it on a Samba fileserver. And there I recognized that the problem only occurs If I downloaded it on a Samba fileserver. If I downloaded files on a Windows Server or onto a Windows Share thats running Windows and not Samba, the file is downloaded correctly. At this point I thought I had found the cause, but that isn't right: The Problem never occurs If I use IE or an older Firefox.

I'm sure that the problem is caused by Firefox in conjunction with Windows Vista and Samba Fileserver, because I never touched the Systems and the problem exists only since Firefox 6. Also look here, if I changed the possible system components step-by-step:

• Browser -> Client OS -> Saved to Filesystem
• Firefox -> Windows XP -> Samba (OK)
• Firefox -> Windows 2000 -> Samba (OK)
• Firefox -> Windows Vista -> Samba (Corrupt)
• IE -> Windows Vista -> Samba (OK)

I also contacted the firefox support, but they can't recognize any problems, because they didn't take Samba in combination with Vista and Firefox into account. I described the problem very detailed but they refused, that it is caused by Firefox. Moreover I run all tests without any plugins and without any addons again and again. I also created a new profile and deinstalled and reinstalled a fresh firefox completely.

But look at my analysis again: Only if you change the variable of the browser the files get corrupted: Firefox is the problem!

The problem still exists in Firefox 10.0.1.!

Have a look at the the filediff: left/top: the corrupt file; right/bottom: the correct file