Hey,
I just got this pop up ad.. not really a pop up though, it just showed up when I was posting and to get back to JM I just pressed the back arrow(so it opened in the same page if that makes sense)
Diaper Swappers had this same issue and I believe it had something to do with one of the ad on the site.. so they stopped all ads except google(or something along those lines).
anyhow here is a screen shot: