why new packages take so long to enter?

[Rafael Rodríguez <rafael.rodriguez.tf@gmail.com>]

Hi.

Many days ago two packages in sid caught my eye: firefox (a replacement for 
the new mozilla-firefox package) and update-notifier. However, a couple of 
weeks later, they still haven't hit amd64's sid. Why is this?

TIA,

Rafael Rodríguez