In Firefox 14.0.1 on Mac, I can’t type the colon ‘:’ in http://typing.io/lesson/clojure/clojure/zip/1 or the underscore ‘_’ in http://typing.io/lesson/ruby/rails/relation/1. I also can’t use caps lock to type USAGE in http://typing.io/lesson/shell/git/git-mergetool/1. But I think moonboots already knows about these problems: https://news.ycombinator.com/item?id=4419357.

FF15/Win7 here, and I'm also having trouble with underscores

Thanks, will take a look into this