of course, microsoft doesn't support nearly as many platforms. mozilla releases 1.0 for the following:
win32
mac os 8.5, 8.6, 9.x
mac osx
linux (x86 and powerpc)
bsd 4.2 4.3 (x86) 4.2 (sparc)
freebsd
openvms
os/2
tru64 unix
the design goals for mozilla are different than ie. nonetheless, it's taken too long. joel on software has a good column on the subject. yes, i know netscape != mozilla, you lurkers.
Well, maybe 2 or 3 official ones. However if you count the number of security updates it has had must be a few hundred. Some people wait rather than putting out garbage.