Iceweasel's rendering faster than Firefox?

[Cassiano Leal <cassianoleal@gmail.com>]

Fellow Debianers,

I have been using Firefox 3.5 since its earlier betas, and although
javascript has been considerably faster than with 3.0, rendering of
pages and especially dragging and dropping on web pages was still
painfully slow in some cases.

I work in the development of a web based reporting application that
has recently had implemented a WYSIWYG formatter that makes extensive
use of javascript for drag-n-drop interactions. This page is blazingly
fast on FF/Windows and Safari, and even on Arora on Linux, but
Iceweasel/FF on Linux was painful to use.

Now, with Iceweasel 3.5, things work quite alright. Not perfect --
Arora/Webkit is still a bit faster -- but I can actually use the
interface.

That leads me to two things. First one: kudos to the Iceweasel team
for releasing a Firefox better than the actual Firefox! :D
Second one: anyone knows where this speed boost comes from?

Cheers to you all!
Cassiano Leal