Firefox releases (based on the train release model) go live every 6 weeks. However, this December instead of pushing a new mainline release, we plan to push a dot release 50.1.0 mid December. This will be a limited scope release and will only include fixes for recent severe regressions, crashes and security issues. The motivation behind this dot release is to minimize code churn and limit unexpected disruption to release end-users during December due to a Mozilla internal event and the holiday season.
50.1.0 release is planned to be pushed to release end-users on December 13th 2016. This dot release will be supported until January 24th, 2017 after which Fx51 release is planned to go live.
The ESR release schedule remains unchanged. ESR45.6.0 is planned to go live on December 13th 2016 and ESR45.7.0 will go live on January 24th 2017.
Cheers, Your friendly Mozilla Release Management Team!