1) right click "Return Game" and choose "Open in a New Tab"
(You should be back now in your game...)
2) click competition (in castings) / challenge (in survivor)
(that should be ok right now)
3) do the challenge
4) save (of course :p)
5) close the tab that "froze"
6) now, continue to use the tab you used in #1
7) if problem persists, repeat steps 1 to 6
