Try to be assertive a bit. :) FF 3.6 has been sticking i.e. with Ubuntu. The concept of Linux is using stable, time-proven software. When you want to guarantee stable browser for the whole environment (i.e. on university or in company), you will stick with something you know that works fine. You won't be looking forward for quick-and-in-hurry-developed new versions. Especially when they come with no visible enhancements or new features – then you start worrying about bugs introduced into the program with update.
Personally I don't have reasons to delay upgrade much (except for incompatible addons), but if I should make a decision for a whole bunch of computers, I would stick with 3.6 too. ;)