Dit staat op de homepage van de backports
What are 'Backports'?
Backporting is the process of compiling and providing new packages for a distribution that no longer gets any updates except for security purposes - for example backports are often made to bring the latest, greatest version of a crucial piece of software to a version of an OS that it isn't officially available for. Specifically, when backporting, the package is taken from the current development version of the OS.
In Ubuntu's case this means that packages that are in the Dapper Drake repositories(the unreleased successor to Breezy Badger) can be compiled and made to run on Breezy.
As a result, in order for a package to be considered for backporting, it must first be available in the Dapper repositories. Failure to check this is probably the main reason for the refusal of backport requests.
En dit staat op het forum van de Backports:
Backports, Dapper and fat packages
So it's not too surprising that Firefox 2.0 will not be backported to Dapper, given all the many interdependies associated with it. Enough said -- it's just not going to happen.