The other day at work, my co-worker noticed that FB was hijacking the console object. When you trying to invoke console.log it would output in big red letters telling you that it was dangerous to paste js into webpages. And offered a url to a page you could turn off the warning.
I just tried it now on my FB account and it looks like they didn't touch my console. My guess is that I've been developing apps on FB since 2007 and maybe i already disabled that via something long ago.
It was something they only ever rolled out experimentally to a few users as far as I know. Having worked on a relatively popular social network before the reason they did it made perfect sense to me. A lot of people are really willing to buy in to the idea that they'll get some special treatment if they say a magic incantation into a thing they don't understand.
Just look at those "Forward this email or Bill Gates will kill MSN/sell your children/make the moon landing fake!" things that used to go around. People fell for them.
I think the most compelling example of this is something called "Freemen on the Land", and related belief systems. Instead of people's ignorance of technology, it exploits their ignorance of the basics of law. Like, did you know the government holds hundreds of millions of dollars in your name in a secret account? If you just say the right magical incantation in court, you can use it to pay off your parking tickets. Many people have believed this and tried it.
If you haven't heard of it before, prepare for a journey through Wikipedia as fascinating as it is pitiful.
According to the stackoverflow link, it appears to be a soak test on certain accounts. If you aren't affected (or if you have developer tools on) it will likely not do this.
They're not trying to lock out web-developers, but normal users that would otherwise never open the developer tools.