I checked and my Mozilla setting is to block pop-up ads. That hasn't been changed.
I used to see pop-ups constantly on Yahoo, where I have an email account. This stopped when I got Norton 360, started using the VPN, with the Ad Blocker turned on.
If I forgot to turn on the VPN, I would see the pop-ups. When I turned it on, the pop-ups would stop.
This changed last week, for some reason.
The VPN is on with the Ad Blocker turned on. Mozilla is set to block pop-ups, and yet, since last week, I keep getting these pop-ups. That wasn't the case before last week.
Malvertising
Malvertising, or malicious advertising, is the use of online advertising to distribute malware with little to no user interaction required. https://www.malwarebytes.com/malvertising/