In my own experience, those little popups that cover the whole page, are the result of you installing something you didn't intend to click on... like the little adverts down at the bottom of free apps.
For me, after about a week of trying everything suggested, the only thing that worked was to do FDR.
that wiped out all of the System Files, and that took care of the popups.
that has been 18 months ago now, I never follow links to anywhere. If I see something of interest, I use Google Search or go direct to the Play Store and download it if it is an app.