Are these empty popups a Flash Player bug or a malware?

Environment:

MacOS X 10.10.4

Firefox 44.0.2

Flash Player 20.0.0.306

For security policy I have also:

NoScript 2.9.0.4

Ghostery 6.0.3

I use the anti-virus clamav (version 0.99) "on request" every day but it isn't a resident anti-virus.

This computer is fully clean.

On the other hand our company network is fitered by an anti-virus and an anti-malware which

no one can turn off (Palo Alto + Ironport).

Since a few days I have regular empty windows which pop up on my work:

These are Finder windows.

(I am trying to find to which event they might be related).

Here are my settings within System Preferences:

How may I diagnose quickly if this is a malware or a Flash Player problem?

Which logfile should I look at?

I am also interested by very similar cases and their technical environment (as given at the beginning of this question).