I use the latest nightly build available, but it isn't working on Firefox 48.0.
Looking at the nightlies page on the website, I see these:
http://5digits.org/nightliespentadactyl-latest.xpi — Latest pentadactyl Nightly
pentadactyl-20160719.xpi — pentadactyl Nightly 2016-07-19
pentadactyl-20160718.xpi — pentadactyl Nightly 2016-07-18
pentadactyl-20160717.xpi — pentadactyl Nightly 2016-07-17
pentadactyl-20160716.xpi — pentadactyl Nightly 2016-07-16
pentadactyl-20160715.xpi — pentadactyl Nightly 2016-07-15
pentadactyl-20160714.xpi — pentadactyl Nightly 2016-07-14
pentadactyl-20160713.xpi — pentadactyl Nightly 2016-07-13
pentadactyl-20160712.xpi — pentadactyl Nightly 2016-07-12
pentadactyl-20160711.xpi — pentadactyl Nightly 2016-07-11
pentadactyl-20160710.xpi — pentadactyl Nightly 2016-07-10
Does that suggest that nightlies are not being compiled any more?