Quoted from http://www.mozilla.org/roadmap/mozilla-1.0.html:
> The first major-revision-number milestone release (mozilla1.0) of the > Mozilla browser application suite and platform from mozilla.org. A > release of higher quality than any delivered so far, on whose quality > our reputation is at stake precisely because 1.0 is such a coveted and > feared version number. It also mentions the API freeze as the second reason and longevity as the third reason for a 1.0.
