I'm in the world and am getting the big black box--I think it's the feat reward itself that's mucking us up and it doesn't matter where we are. :)
ETA: not sure if it made a difference as to browser, but my alt got in just fine on Chrome, and she participated in the feat as well. I'm going to try to log VS in on Chrome (rather than firefox) and see if that makes a difference. Likely not, but lessee...
ETA: Yeah. Not browser. Seems to be character-based for sure. Awwww.