Very nice list. I would also add the ability to associate breakpoints with DOM elements. As in "break on any attempt to read/modify a given element". That would be extremely helpful in debugging the hodge-podge of Javascript libraries that many modern web pages are.
The break on modifications should already be possible, by adding breakpoints to Mutation Events (as you can do already with e.g. mouse related events).
However, Mutation Events were marked as deprecated by allegedly bad design. We should be using MutationObserver[1] instead (which, I believe, will be equally helpful in observing changes).
