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).
Sorry, I had it partially wrong. There‘s the C++ Interpreter and the baseline interpreter (that one was added only recently[1]), and then the two JITs (BaselineJIT and IonMonkey). I understand that IonMonkey itself has two levels chosen depending on code hotness.
I.e. these settings will kill all JITs (so the highest 2-3 tiers) and leave the two interpreters.
