How to Disable Automatic Virus Scanning in Built-in Download Manager of Mozilla Firefox?

If you are using Mozilla Firefox, you might have noticed that its built-in download manager scans the downloaded file for virus or spyware upon completion.


Actually this kind of behavior only occurs under Microsoft Windows OS because it uses the antivirus software installed in your Windows to scan the file. If no anti-virus software is installed, it'll not scan the file.

Sometimes it might become annoying for you and you would like to disable this automatic scanning as it takes a few extra seconds to scan the file and it also causes following problems to a few users:

  • The built-in download manager freezes while downloading a file.
  • It doesn't download a file and gives warning message: "Blocked: Download may contain a virus or spyware", even you are sure that the file is completely safe.

So in this tutorial, I'll tell you how to disable this automatic virus scanning to get rid of these annoying problems.

1. Open firefox and type about:config in the addressbar and press Enter. It'll confirm, click on I'll be careful, I promise! button.

2. Now type scanwhendone in the Filter box. It'll show a single entry "" in the results window.

3. Either double-click on this entry or right-click on it and select "Toggle". It'll set its value to "False".


4. That's it. You have done. Now Firefox will not scan any downloaded file and you should not face any freezing problem.

PS: If you can't find the entry, you'll need to create it manually. Right-click on empty area and select New -> Boolean option. Set its name asĀ and set its value to false.

Share this article: Facebook | Twitter | Google+ | Reddit | Tell a friend

Posted in: Mozilla Firefox, Troubleshooting

Other similar articles that may interest you


  • After filtering I have two entries:
    Should I disable both? (Firefox 10.0.2 on WinXP Home edition, both Hungarian)

  • VG

    ^^ You can disable both.

  • Hey VG, whenever I click on a download link, the browser freezes till the IDM download window appears. How to fix this?

    I'm using Firefox 30 and IDM 6.20. Windows 8.1 x64.

  • VG

    ^^ It seems a problem in IDM not in Firefox. You can try a re-installation of both software. Sorry but there is nothing else which I can suggest.

  • I tried reinstalling both but not helping. Tell me if you find something useful regarding this.

  • i typed about:config, and then searched scanwhendone but nothing shown up.
    what is the problem of mine? im using the newest firefox

  • VG

    ^^ You can manually add it in prefs.js file:

  • can you please provide the newer version keys?

    i saw those 3 that seems related( using the 'download' keyword): ( i just want to set it for a one time download and to be able to reset it back) any suggestions?

    urlclassifier.disallow_completions : | default | string | test-malware-simple,test-phish-simple,goog-downloadwhite-digest256

    urlclassifier.downloadAllowTable : | default | string | goog-downloadwhite-digest256

    urlclassifier.downloadBlockTable : | default | string | goog-badinurl-shavar

    running firefox 32.0.3

  • when I type scan in the filter box, nothing really shows up.. please can I disable mozilla from blocking my downloads?

  • VG

    ^^ Create it manually. I have updated the tutorial.

Leave a Comment