When I was browsing (a local copy of a site off my own hard drive), I was greeted by a pop-up that took up the entire bottom half of my screen that detected that I was on the site that had a menu of specials, and this pop-up basically counter-offered me other specials from our client's competitors.

A smaller, similar popup came up on the bottom right of my screen later and made reference to savings.com.

I noticed a new Firefox extension I'd never seen: BetterSurf 1.0. Date it was updated? TODAY.

I'm guessing I somehow got some malware. Could have come from a Firefox or Google Chrome update installation, or perhaps it was from when I downloaded and installed NetBeans 7.4 a couple of weeks ago. (Why, then, would this situation manifest itself NOW?)

I ran MalwareBytes Antimalware (came up with over 100 suspect objects!) and rebooted. I'm not getting the pop-ups any more, and I'm also not seeing any of the subdirectories in C: that are mentioned in any answers.

What is this extension and why did it appear?