From FF v7.9, both Nashorn and Rhino Javascript engines are deprecated. From v8.0 they are both removed; only the J2V8 is left. See #5489. J2V8 is not actively supported/improved anymore. Secondly, it does not have support for ARM CPUs on MacBooks with Silicon hardware, for example.

Todo: add a new Javascript Engine to FF!.
E.g. inspect if GraalVM Javscript is possible as library. It seems to have good compatibility with Nashorn.
Business value: check if users of FF! are waiting for a new engine.

Background JS options:

• https://github.com/caoccao/Javet
• https://github.com/oracle/graaljs
• https://towardsdev.com/performance-comparison-of-graaljs-javet-and-nashorn-7bae6925826a