Disable Automatic Virus Scanning in Firefox

Martin Brinkmann
Jun 4, 2008
Updated • Apr 27, 2014
Antivirus, Firefox

Firefox 3 is making use of the installed virus scanner on Windows to scan downloads automatically after they have been fully downloaded to the system.

This feature is only available on Windows and if an anti-virus application is installed on the user's system. While this feature may be a good way to avoid downloading malicious files it ,ay on the other hand be the source of complications like delays, freezes or that harmless files (false positives) are blocked by the anti-virus software.

I personally do not think that such a feature is necessary due to the real-time protection that most anti-virus applications provide anyway, as they will scan the file when it is launched on the system.

The Mozilla team created a new preference that gives Windows users the option to disable the automatic virus scanning in Firefox which comes in handy if you have a anti-virus software installed but do not want it to scan the downloads or encounter issues because of this.

Type about:config in the Firefox location bar and filter for the string browser.download.manager.scanWhenDone. The default value of that parameter is true which means that scans will be done whenever a file is downloaded. Setting it to false will disable the automatic virus scanning in Firefox 3.

firefox download disable virus-scan

During research I came upon another error that is connected to the Download Statusbar extension. If you receive the error message Anti-virus Program not found after a download completes in Firefox 3 and have the Download Statusbar extension installed you need to set the path to the anti-virus program manually in the Download Statusbar options.

Please note that the virus scanning works in newer versions of Firefox as it did in Firefox 3. It is enabled by default in Windows, and to disable it, you need to follow the steps outlined above.

The only difference to Firefox 3.6 and earlier is that setting the preference to false will also disable Windows security policy checks.


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  1. Declan said on March 29, 2014 at 2:21 pm

    Martin, Thanks for that explanation, that was happeneing to me as well.
    And forgive me if I’m piggy-backing here … but do you or any of your readers know of an encryption app where you can encrypt just a singular file? The applications you mentioned above will create a virtual drive or volume to encrypt it, or maybe a virtual folder, but I’d love to be able to encrypt just a file and park it anywhere on my hard drive or thumb drive and know it’s secure.
    Thanks again for your great website.

    1. Martin Brinkmann said on March 29, 2014 at 2:25 pm

      You can use a program like Datalocker for that, or zip software such as 7-Zip.


  2. PhoneyVirus said on March 30, 2014 at 3:18 am

    Had to remove the beta, because I having problems with Real-time protection. I did like the layout, but everything was pretty much the same. Looking forward to the stable version when it releases, when ever that maybe. Also like the ideal of them supporting TrueCrypt because I use it. There’s one thing that I hate about Malwarebytes and that is, it never remembers the last window size when closing it. Kinda annoyance when using it on a smaller screen, say like a Netbook.

  3. Declan said on March 30, 2014 at 5:46 am

    Thanks, Martin. I’ll give it a try.

  4. [email protected] said on March 30, 2014 at 4:19 pm

    Scanning your hard drive for Adware Tracking Cookies is unnecessary. It will wear out your hard drive sooner and wastes your time. Keep the following folder in Windows Explorer emptied out. I check mine once a day. Add the folder to your Windows Explorer Favorites.


  5. chesscanoe said on March 31, 2014 at 3:54 pm

    https://www.malwarebytes.org/support/guides/ has a MalwareBytes User Guide you can click on to read in your Chrome Browser (at least). You then can get directions to exclude files and folders individually. Wouldn’t this circumvent the encrypted files problem? ( I don’t have any to test).

    1. Martin Brinkmann said on March 31, 2014 at 3:57 pm

      It is not a problem of encrypted files, but of encrypted hard drives and partitions.

  6. Joe C said on December 27, 2014 at 7:54 pm

    I’m getting the same ‘can not load Rootkit driver (error 20025) on a 13 year old Win XP system after an upgrading to 2.0) yes, I know I need a new PC and am accepting donations HAHA) I’m running the stock program configuration because I haven’t figured out how to change anything (I’m visually impaired and the current UI makes this difficult) OR amake this error go away. I have no encrypted drives that I know of. I WANT to do a rootkit scan so the prompt to run the scan without it is useless. I’m running Zonealarm and Avast, AAV’s scan completes with no issues. In spite of these I’m pretty sure I have a rootkit and am trying a Shotgun approach, most AntiRootkit tools find no issues. Please, guys, I’m going bald from tearing my hair out over this one. Perhaps MWBAM is choking on an older stsyem? The other AntiRootkit utilities (RootkitBuster, Kapersky, Combofix, et.al.) can’t find that much but run just fine. I’m NOT running in Safe Mode, I’ll try that later. If that’s the fix, maybe MWB will include specific instructions to that effect — or write a truly automatic program. Now that Microsoft has cut us adrift we are at the mercy of wind and weather, we have no other course to chart. Thanks for any bearings, Joe C

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