Firefox doesn't virus check downloads with Microsoft Windows Defender?

It has recently come to my attention that Firefox does not virus check downloads when the user is using Microsoft Windows Defender as their virus checker.

I’m not quite sure how this is even possible given that MS Defender apparently intercepts writes to the filesystem at a low level, and I had blindly assumed this to be the case but was recently shocked to find a file that containing a (false positive so no harm done) virus was detected by Chrome via MS Defender but not by Firefox.

I confirmed this with the EICAR files - again, Chrome/MS Defender caught them, Firefox didn’t.

I have talked to Firefox users with 3rd party AV software and their downloads apparently do get checked, but plenty of people including myself are happy with MS Defender and have no desire to introduce yet another system hogging, AD spewing virus checker into their system.

Perhaps there is a system setting to enable this, but I’ve looked and I can’t find one. The about:support page even specifies ‘Microsoft Defender antivirus’ under ‘Antivirus’ so it feels like it should be working?

Or perhaps my Firefox has itself caught a virus?!

But if this is a bug or a WONTFIX, please, please, please don’t give me yet another reason to migrate to Chrome and fix this ASAP!

I am running Firefox 124.0.2 (64-bit) on Windows 10.


This forum isn’t very active and posting here isn’t a good way to reach the developers.

Two ways to make suggestions to Mozilla:
• Suggest the idea with Mozilla Connect.
• Report the issue in Bugzilla.

I found a similar issue in Bugzilla, but it is for AVIRA Antivirus.