Hello,

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from http://www.mozilla.org and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (click Exit from the Firefox or File menu).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not run Firefox's uninstaller or use a third party remover as part of this process, because that could permanently delete your Firefox data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be recovered unless they have been backed up to an external device!

Please report back to see if this helped you!

Thank you.

It is possible that anti-virus software is corrupting downloaded files or is interfering otherwise.

Try to disable the real-time (live) scanning of files in your anti-virus software temporarily to see if that makes downloading work.

See also:

• http://kb.mozillazine.org/Unable_to_save_or_download_files
• browser.download.manager.scanWhenDone = false

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Sometimes during a download, Firefox thinks the download is done and closes the download. Why? I don't know. I suspect many reasons, but have no way to check them. All you can really do is download the file again. Also, see if the file is available at another site.

@Jackson1442: A clean install produced the same results. As I noted in my original post I already had a clean profile. Doing a clean reinstall and a clean profilee produced the same results. Some downloads finish, some will fail to finish but be labelled as complete.

@cor-el: I do not have any anti-virus software, so that shouldn't be the problem. I went ahead and added the scanWhenDone variable anyway (it did not exist by default) and it didn't change the results. Downloads will still fail and will be labelled as complete.

@FredMcD: That's not good to hear. This doesn't happen at all when using Chrome, but I do not want to use Chrome. I prefer to use Firefox as I feel Firefox better suits my needs. However, not being able to tell if a download has really completed or if it has really failed is crucial. I would hope someone out there knows a solution, or at the very least this is being worked on to be fixed.

See also: Unable to Save or Download Files on kb.mozillazine.org

Did you try to boot the computer in Windows Safe Mode?

@Jackson1442: Unfortunately nothing in that KB helped. Most of the KB was general Firefox resetting which I have already done in regards to completely starting both a new profile and a fresh install of Firefox. The Windows related items did not change the results.

@cor-el: Windows Safe Mode made no difference, nor should it. This is not a Windows issue. When Chrome, Internet Explorer, Opera, etc. all can finish downloads properly and Firefox is the only browser with the issue, Windows is not the issue. The files being downloaded are over a GB and are usually anywhere from 1-5 GB. Small files in Firefox go well because they finish before this issue has a chance to occur. Large downloads have a bigger possibility for "Download complete" failure.