Firefox for desktop gets updated every 6-8 weeks. The 2016 Firefox release schedule is below. And you can find the Rapid Release calendar at https://wiki.mozilla.org/RapidRelease/Calendar which has the upcoming release dates/moving from branch-to-branch.

2016 Firefox Release Schedule 2016-01-26 – Firefox 44 2016-03-08 – Firefox 45, ESR 45 (6 weeks cycle) 2016-04-19 – Firefox 46 (6 weeks cycle) 2016-06-07 – Firefox 47 (7 weeks cycle) 2016-08-02 – Firefox 48 (8 weeks cycle) 2016-09-13 – Firefox 49 (6 weeks cycle) 2016-11-08 – Firefox 50 (8 weeks cycle) 2016-12-13 – Firefox 50.0.1 (5 week cycle, release for critical fixes as needed) 2017-01-24 – Firefox 51 (6 weeks from prior release)

Sometimes there are "chemspill" releases made, too, at irregular intervals as needed. Rather than waiting for the next full release data to fix important security faults that are discovered between releases or to fix other problems of importance to a large number of users - a "chemspill" release might be made. As with the recent Firefox 46.0.1 release.

thanks so much for your help guys.