> A minor upgrade to 3.9 is 3.10, whereas going from 39 to 40 makes no such distinction.
Just like in the kernel development model, Firefox releases happen every N months. There are no "major" updates, just time-based releases which include whatever features were ready in time for integration.
Most Linux distributions work this way, which is why we have Fedora 16 and RHEL 6. The yy.mm numbering scheme used by Ubuntu and OpenSUSE does not have anything to do with major and minor releases.
> In analogy to your question, I could ask: Why write dates as year-month-day?
> Why not simply count days from some arbitrary starting point?
Indeed, that's an unnecessary complication originated when the motion of celestial bodies was attributed to divine will and incomplete astronomical knowledge. Still, dates expressed in yy-mm-dd format have at least some relationship with actual cycles of our planet. What would a major.minor version scheme mean in the context of Firefox's time-based releases?