I would love to see a JavaScript debugger that could break to something like an ipython shell. It's the one thing I really miss moving from server side to client side debugging.
The main difference is the ability to interact with objects in the scope of the breakpoint. The console is always in window scope and I want to interact with local variables within a certain function.
If I don't misunderstand you, you can do this in Firebug. Open one of the scripts in the Script panel, click on the left hand side of any row to set a breakpoint. Execution will break there, and you can inspect the call stack, local scope and everything.