First of all, I apologize for calling Mozilla 'old Mozilla', it is just that many people refer to Firefox as just Mozilla and I didn't want to cause confusion.
The Debian version of Firefox is modified slightly. But that can't be the reason for such a dramatic difference in speed (yes, I do agree with you). As a matter of fact, I think the main reason is actually hardware. Windows is a very bloated piece of software (if it can even be called that), and therefore, most computers with it installed are reasonably fast. Debian, on the other hand, (and most other Unixes/Linuxes for that matter) can run on much slower machines. For example, I have a friend that has 3 computers in his room, Windows ME, Windows XP, and Debian. Windows XP is a state of the art computer suitable for gaming, the Windows XP is usable if not fast, but the Debian is slow. This is not because he does not like Debian (he does) but because Debian can easily run on slow machines. Therefore, when someone installs a pretty big piece of software (Firefox), it runs pretty slowly. In any case, I apoligize for sounding so inconsiderate of a high quality piece of software that now has a successor Leonid Grinberg
