speed - mozilla/i.e

How come pages are so much faster on mozilla firefox(3.0.5) than i.e 6.0

Is it because mozilla has less security patches than i.e. or ?? thanks

I have asked the same question in a conversation with our developers and the short answer is that Mozilla’s JavaScript engine is simply superior to IE’s implementation in terms of performance. We are working very hard on achieving performance parity between Firefox and IE, but the IE engine is unfortunately making it very hard for us.