Q: Why am I getting pop-ups and pop-unders when I have do not allow pop-ups checked in my preferences?

    I am getting an extreme amount of pop-ups all of a sudden - seemingly out of nowhere.  I've been using my Macbook for about a year and a half and this is unprecedented.  The only thing I can think of is that there had recently been an outage in coverage in my local area.  It only lasted a few hours, but after my service was restored was when this started happening.  I don't know why, because my service has cut out before and this never happened before.  I have double, triple and quadruple checked my browser settings on Safari, Chrome and Firefox.  They all have the box checked that says do not allow pop-ups.  I haven't noticed it really with Firefox, but with Safari and Chrome they are incessant.  It's almost always a full screen-sized window popping up under the browser that I have open, but sometimes opening a new tab in my browser also.  This is sometimes even happening without clicking on an actual link even.  How can this be and how can I stop it?