[roca]

Releases are almost always date-based, but once in a while a release is delayed. I guess that's a bit easier if the release number is not a date.

[glandium]

There's also the fact that Firefox is now on a 4 weeks release cycle, which means there will be months with two releases. (and that's ignoring chemspill releases)

[afiori]

Then if not year.month they can use year.counter where counter goes from 1 to 14 = ceil(366/28)

[throwaway2048]

i mean, whats the problem with the version going up 2 numbers rather than 1?

[roca]

It's suboptimal to have to change the number of the next release during a release cycle. That would mean, for example, that Firefox Nightly 2020.11 might correspond to a Firefox release 2020.12.