Ok, I think I recall the issue, though it could still be a number of things...
The first thing I'd check, though, is to see if disabling the Disqus plugin solves the problem. I believe I've seen this error before with that plugin, and I can see that it's causing the issue on Android browsers as well, so I think it has something to do with that.
If, after you disable Disqus, you see that the box goes away, you can still use Disqus, but I believe you may have to do some testing with their options to find a configuration that won't cause that issue. I think there's a mobile theme they offer that can be enabled/disabled, or you can try a different theme.
I'm still relatively certain it's Disqus, but let me know if it's not.