Why do I keep getting this virus popup from Avast when I start Firefox?

I tried scanning my computer multiple times and it doesn’t find any problems whatsoever, but I still get these popups almost every fifteen minutes.

https://forum.avast.com/index.php?topic=53253.0

exact same problem here!!

probably false positive

I’ve same problem. I guess it’s a false positive? Waiting news from AVAST specialists…