I think where there used to be two settings to give one finer control over things there is now only one. IOW, I think scanWhenDone didn’t affect windows security policy checks in the past but now it does. For reference:
Unable to save or download files page @ Mozillazine (may be having some probs atm)…
http://kb.mozillazine.org/Unable_to_save_or_download_files
Google cache of the above…
http://webcache.googleusercontent.com/search?q=cache:JExXaHkix1wJ:kb.mozillazine.org/Unable_to_save_or_download_files+&cd=1&hl=en&ct=clnk&gl=us&source=encrypted.google.com
I’ve verified that Launching applications and unsafe files, when set to disabled, causes my downloads to be canceled. If I temporarily flip it to prompt they work. Shrug.
FWIW, after I posted I thought to try downloading one of the easier eicar test files (eicar.com for example) via HTTPS. Regardless of how I adjusted the settings I previously mentioned, Avast detected the threat. Although at times there was a tiny lag as if Avast discovered the new file via a periodic filesystem change report rather than the scan being immediately triggered once the download was complete. I don’t know enough about how Avast works, quite frankly, to confidently test things.