Aaaack, I did something

Not sure what I did, apparently clicked on something that opened a door for pop-up ads. Happened while I was surfing and clicked on the 'shop now' button for a product; didn't buy anything and clicked out. Within minutes, ads showed up whenever I clicked on one of my favorites; not the little popup flags, this time they appear to be a whole site tab, and I can make them go away by clicking on the 'x'. But it's danged annoying, especially when I go to check my bank balance and the screen that comes up is one of those scary "OMG you're being ripped off" things.

I went to settings and deleted a couple of recent downloads, but I haven't been able to find anything else for the dates affected (essentially Oct. 1 forward). Any hints on where else to look, or how to rid myself of this annoyance?

Thanks in advance. Again. And again.

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