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 "browser.download.manager.scanWhenDone" 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.
Posted by: Vishal Gupta | Categories: Mozilla Firefox, Troubleshooting
Uncle G.
After filtering I have two entries:
"browser.download.manager.scanWhenDone
services.sync.prefs.sync.browser.download.manager.scanWhenDone"
Should I disable both? (Firefox 10.0.2 on WinXP Home edition, both Hungarian)
VG
^^ You can disable both.