[FooBarWidget]

What does 10% faster mean? When people talk about "performance" I'm sure that most of them actually mean UI responsiveness, not raw number crunching performance. How do you measure that and what does 10% in that context mean?

[sayrer]

It's actually around 10% faster at a bunch of things. :) This includes some DOM APIs and just raw JS perf, depending on your platform.

Responsiveness will be improved in a different manner. We are working on a bunch of improvements for later in 2011 that should make a big difference. I think Firefox 4 is in general much better than 3.6, and I expect to see parallelism, responsiveness, and reliability continue to improve.

The big ticket items are multiprocess browsing and better debugging APIs--we have an issue with developer extensions causing performance problems. This is not necessarily the fault of Firebug or any of the other extensions. We need a better foundation for them to build on, and it really hurts us to give developers a slow experience.