Why? What's even the point for the year.month version numbers? I know ubuntu uses that, but as far as I'm concerned it's a completely useless complexity, the first half increments half the time, and the second half repeats non-stop, parsing that is actually more annoying than a straightforward "is 22 bigger than 19?".

Not to mention the ultimate goal (of Chrome and Firefox both) is probably to have "version number" fade away for everything but debugging/problem checking, users shouldn't have to care, the browser is "always up to date" and that's that.