Latest Android Nightly build is 68.0a1 from 2019-05-04.
Latest Android Beta build is 68.0beta, from May 21, 2019 (actually from APK name it's 68.0b11).
Latest iOS Release build is 16.0, from April 15, 2019.
By the way, latest Desktop Beta build is 68.0beta, from May 22, 2019, and latest Desktop Nightly build is 69.0a1, from May 20, 2019 - and there's no information about whether they affected too.
The iOS version should be unaffected, as Firefox for iOS does not include its own JS engine (it uses the one provided by the system), which is where this vulnerability is.
For the Desktop version at least, if you download the current beta (68.0beta11), you'll notice that it was built two days ago. The latest nightly was built today. The changelog for these is just not kept up to date.
