Not everyone has the permission to install the latest browser or any adblock. When I was having this problem it was definitely coming from the unblocked ads on a paleolithic browser. I never saw it with a current browser and haven't had it since upgrading membership.
Meanwhile, anyone ever get the one where you go back a page and the entire page is copied into the reply box somehow?
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Genesis 49:16-17
"Well, well!" said Holmes, impatiently. "A good cyclist does not need a high road. The moor is intersected with paths and the moon is at the full."