Ah, sorry, I hadn't twigged we were talking Firefox here.
Your timing as to when it happened coincides roughly with the arrival of the latest release for desktop Firefox. I don't know if the iPad versions of Firefox are in lock-step with the desktop versions, but it might be worth checking the version history.
edited to add: Just grabbed the latest iPad Firefox (20.1) and, yes, it's doing it here too. So it's not you, not your iPad, but dear old Mozilla.