Text Enhance suddenly on almost all websites

I woke up this morning, and nearly every Web site I visit, including several of my own, now have text enhance ads, the kind where a word or two is underlined and if you hover your mouse over the underlined word, an ad displays. So it looks like I've been infected somehow. This is affecting both Safari and Firefox.

I tried resetting Safari as far as getting rid of the cache and all cookies, but that didn't do it. Anyone else know about this or what to do about it?

Thanks.