I've been rehabilitating the old ppc64le JIT against more current Firefoxes and there is now available a set of patches you can apply to the current 115ESR. This does not yet include support for Ion or Wasm; the first still has some regressions, and the second has multiple outright crashes. Still, even with just the Baseline Interpreter and Baseline Compiler it is several times faster on benchmarks than the interpreter-only 115. I've included also the relevant LTO-PGO and WebRTC patches so you can just apply the changesets numerically and build. The patches and the needed.mozconfig
s for either building an optimized browser or a debug JS shell (should you want to poke around) are in this Github issue.
While this passes everything that is expected to pass, you may still experience issues using it, and you should not consider it supported. Always backup your profile first. But it's now an option for those of you who were using the previous set of patches against 91ESR.