I managed to fix the JavaFX error that was coming up on my Windows 8. I'd previously installed Java 8 64 bit, then 32 bit. NEM would never install, it always stopped with a JavaFX error no matter the browser tried, nor after reinstalling Java.

I uninstalled Java 8, ran CCleaner and did registry fixes and general cleanup. I downloaded the online Java 8 32 bit exe, ran it, removed Ask of course.
Tried the one click install, and it worked this time once Java 8 was authorized in Firefox.