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Downloads with Firefox are not virus checked after download (Windows Defender)

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While doing some virus discovery tests with Windows Defender and other AV products I realized that with Firefox files are not scanned when download finishes. With Chrome and Edge the Windows Defender immediately checks and blocks malicious files. Not so with Firefox. Then the file is only checked and blocked when opened.

After some research I found that in the past there was an Option `browser.download.manager.scanWhenDone` but this seems no longer available. Under Security software in about:support Windows Defender seems to be correctly set.

Is there a way to have files immediately checked by the AV after download in Firefox completes?

While doing some virus discovery tests with Windows Defender and other AV products I realized that with Firefox files are not scanned when download finishes. With Chrome and Edge the Windows Defender immediately checks and blocks malicious files. Not so with Firefox. Then the file is only checked and blocked when opened. After some research I found that in the past there was an Option `browser.download.manager.scanWhenDone` but this seems no longer available. Under Security software in about:support Windows Defender seems to be correctly set. Is there a way to have files immediately checked by the AV after download in Firefox completes?

All Replies (8)

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The tags show Linux erroneously as I made this post from Linux. It's about Firefox on Windows of course. Can someone with sufficient rights fix the tags? It's about Windows and the latest FF Version.

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I think Defender should scan all files as they are written, but maybe the application needs to trigger that? As you probably noticed, Firefox creates a temporary placeholder and the actual download is first saved as a .part file. Can you tell whether Defender is scanning the .part file?

I removed the Linux tag; can you add your Windows version using the Tags box to the right of the question (type Win to generate matches)?

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All security software is supposed to block the EICAR test file, so you can use that to see whether it survives the on-download scan:

https://www.eicar.org/download-anti-malware-testfile/

I get a zero byte file and a yellow triangle on the Downloads button (indicates the download failed or was blocked), but I'm not using Defender.

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jscher2000 - Support Volunteer said

I removed the Linux tag; can you add your Windows version using the Tags box to the right of the question (type Win to generate matches)?

I can't find a way to add tags. Tried edit this question.

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Not working

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damonsalvatorev975 said

Not working

Are you confirming the issue or what are you refering to with "not working".

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I added a tag for "Windows 10"

I can't test Defender due to having other security software (IT department managed).