My assumption is IP address because turning on my VPN works, even with uBlock still on, for Firefox. Unless it's in tandem with a user agent/browser used. Idk.
All I know is launching Firefox vanilla leads to the results in the screenshot now, and it never did before. Turning on my VPN fixes it, using a different computer fixes it, or turning off adblock fixes it. Which leads me to believe there is some form of identification/sniffing/blocking going on for me.
TC is right, a quick google search says this is happening here or there very recently. I'm one of them. Did you guys think they'd just stop with the popup? Net neutrality is dead, and we're about to head into the wasteland of it. We'll see where this blows in the next week or two.
Since only from below can one better see the heights.
http://i.imgur.com/OhZgm.jpg