I had to wait until the end of the article to see that FF4 is still one monolithic process. Everything else aside, that means I still have to restart it occasionally to get memory back. And the tab-of-death problem remains.
They do have Flash isolated, which has solved my main "tab of death" issue. However, I'm probably not a good example here, because I haven't had FF crash in months, at least. I honestly can't remember when it did last crash, except that the only ones I can think of involved Flash.