Malware issue?
My son's laptop runs Firefox, and lately it's been displaying a popup ad along the top of his browser window just below the address bar. The content varies, but sometimes its an ad and sometimes it's just a white bar. AdBlock doesn't seem to recognize it.
I just ran Malwarebytes with a fresh update, and it didn't find anything. However, I discovered that his Firefox now sometimes opens a popup window with an obviously fake warning about possible infection.
It urges the user to call 855-753-9334 for support.
Any suggestions, other than the usual "get a Mac" or "you should run Linux" options, of course?
He knows not to click on ads, and I'm pretty confident that he wouldn't knowingly have clicked to accept any downloads or installs without checking with us first. Mostly he watches YouTube videos about luxury cars, Minecraft or Mario Kart, so it's not like he's scouring the net for malicious code.
Your insights are most appreciated!
= new reply since forum marked as read
Spybot Search & Destroy is the bomb. 
It wasn't the solution in this case, but I've previously had Firefox issues that were resolved through a trial-and-error process of elimination with the add-ons.
