Be aware that this will disable two tiers of JS acceleration (JITting): The lowest level (BaselineJIT, introduced only recently) and the highest level (IonJIT for very hot code).
I.e. these settings will kill all JITs (so the highest 2-3 tiers) and leave the two interpreters.
[1] https://hacks.mozilla.org/2019/08/the-baseline-interpreter-a...