It's possible that it's broken if you're using the nightly... C9 has a history of checking to see if you're using "Firefox" to determine if they run certain Javascript or not, so it breaks on nightlies, which call themselves Minefield or Shiretoko (for 3.5) in their user agents.
I haven't seen this behavior in any Firefox branded release (any of the betas or RCs), but I haven't used nightlies since the last site update; they could have easily broken something.