@ -midnightWell you said in your first post you got this even when not using the browser.
I get this popup several times a day even when I don't have a browser open.
So that is somewhat inconsistent from what you are saying now.
I only get these popups when I'm using Firefox.
As has been stated the most likely reason is a bad add-on trying to connect to a site considered malicious by avast. So you should follow up on the advice and submit the logs so that it can be found and resolved.
I know I don't have a virus or malware on my computer as I scanned with Malwarebytes and Avast quick scan.
Otherwise what is the point of of seeking help/feedback in the forums if you aren't going to follow it.