Beware if you see this Scam appear when using IE11. (I don't have Mozilla either anywhere on the system).
Clean your machine Immediately -- DO NOT click any links, Close browser down immediately as well as any applications you are running and either clean your machine with whatever AV software you have or (preferably) restore from a clean image.
Malwarebytes usually pretty OK didn't detect anything amiss.
I always prefer to do a complete restore from a clean backup.
I can state that the ONLY sites I've logged on to this morning have been
1) BBC -- I'm sure that's clean
2) Windows 10 Forums --I'm also sure that's clean
3) Google --> who knows what's there these days
4) Zoopla UK Real estate search with links to Real estate agents / brokers
Could have been 3 or 4.
Ist time in over 20 years of using Windows that I've had this type of nonsense so TAKE CARE everybody.
I'm Thinking of going back to LINUX for Internet browsing. I can't understand why Malwarebytes didn't pick up this piece of malware or "Malvertising".