Mostly what the benchmark shows is that the benchmark in question measures one specific thing which doesn't have a JIT fast path in Firefox yet, but measures it multiple times in different ways...

[Edit: Actually two things: hot loops in the same function as a class definition, and derived classes that use "super".]

Chances are whatever you see on your app is a different issue. I'd be happy to profile and file bugs as needed if you can get me a link that shows the problem on your app.