HN user
To be precise, code caching has been in major browsers for a while, but it was in-memory cache. Chromium is the first to make it persistent with this update. Yet, what's cached contains no optimization result. It is more like basic parsing and translation into machine code.
There have been many different VMs implemented on top of JavaScript VM, and it is to be able to run codes written in different languages on JavaScript VM without porting effort. It is useful since there are systems only running JavaScript programs, such as web browsers. I guess the purpose of this project may be justified similarly as Go started off from frustration with JavaScript and Go enthusiasts are dreaming that it would replace JavaScript (or get a spot in every browser) in the future.
Thanks. I found it. http://www.ghacks.net/2015/02/18/firefox-38-notifies-you-abo...
"The problem is bad enough that a future version of Firefox will even have a feature dedicated to letting you know which of your add-ons is slowing you down."
Does anyone know this feature of Firefox?