Starting with step 3, the apps embedded in the code lab are slightly broken in Firefox 31 Beta. They're fine in Firefox 30 and every other browser I've tried.

This is being discussed on reddit:
http://www.reddit.com/r/dartlang/comments/28crq2/bad_luck_brian_wants_to_learn_dart/

I tried regenerating the code, but it didn't help:
https://chromiumcodereview.appspot.com/339243004/

To reproduce the problem:

1. Go to either https://www.dartlang.org/codelabs/darrrt/ (original generated JS) or
   https://newjs-dot-dart-lang.appspot.com/codelabs/darrrt/ (newly generated JS).
2. Click the link for Step 4.
3. Scroll up until you see the name badge.
4. Type into the field.

You should see what you type appear in the name badge. In Firefox 31 (on Mac & Windows, at least), you see no change in the badge. There's an error message.

Old JS error message:
TypeError: J.getInterceptor$x(...).get$target is not a function piratebadge.dart.js:5650

New JS error message:
TypeError: J.RE(...).gN is not a function piratebadge.dart.js:2963

In other respects, the app works. Perhaps this is a Firefox bug that we can work around and/or help them fix?