Rapid development leads to many incompatible AddOns

Hi to all,

directly spoken: One of the most interesting features of FF - the
AddOn's - get more and more often problems because of the method(s) of
FF's development.

Although development in general is necessary, of course and very
important.. but I don't understand, why some basic functionality (for
example some interface modules als well as JavaScript, I assume)
changes that quickly.

Many AddOn's need significantly more time for updates and in the
moment even some well-known AddOn's like DownThemAll do only support
FF 6.X, although there are 4 (!) complete new 'levels' of FF versions
in nightly available (7.x, 8.x, 9.x, 10.x). Even the releases begin to
outspace some AddOn's.

Ok, my question: Why is it necessary to change so many aspects in a
way, that make make it essential to rewrite so many AddOn's with every
new 'major version step' (e.g. 6.x to 7.x)? I don't understand, why it
is so important to make several steps during one year (it is really
very strange - sorry - to see FF versions ranging between 3.x and 10.x
in use... even though some of them are only nightly's and some others
are known to be outdated... it looks like an inflation in versions).
Well done software need to be updated as well, but not permanently
from ground up - sorry. It looks like there is a preference in
development... and speed in development seems to beat quality
completely. Can this really be a good idea...?