Today, when I returned to a web page opened in Vivaldi on my 18.04 laptop, after a few seconds,the screen was mostly obscured by a large pop-up to sign in to my Yahoo account, one of my less used emails. I clicked it on the upper right x to close it and resumed my reading. After a few seconds this repeated. And then the same behaviour several times more. Clicking on 'help' rather than 'x' didn't get me anywhere. That pop-up keeps appearing. I closed the browser and re-opened it. Same thing. I closed everything on the computer and restarted it. When I returned to the page I was trying to work on the problem remained the same. I only use Yahoo for receiving emails. I'm never asked to sign in. I closed everything and opened Firefox. Before I could even go to any page, that Yahoo sign-in page dominated the screen. I tried closing it with the x a few times. Sometimes it reappears after two or three seconds, sometimes after several more. I closed everything again, restarted, and opened Software Updater. All software is reported to be up to date. I opened Firefox again to find the problem still there.
When I moved to my Ubuntu 20.04 desktop, where I am typing now, in Ask Ubuntu opened in Firefox, I haven't seen any problem. Has anyone else had this problem? I'm baffled.
