Type Inference is additional code that analyzes JS both globally and locally for types, and feeds that info into the JITs to make them more effective.
Previously Firefox used TraceMonkey, then TraceMonkey+JaegerMonkey, and now JaegerMonkey+Type Inference. The plan is to move to IonMonkey+Type Inference (not sure where JaegerMonkey fits into that).
JaegerMonkey is a method JIT.
IonMonkey is an SSA-optimizing JIT.
Type Inference is additional code that analyzes JS both globally and locally for types, and feeds that info into the JITs to make them more effective.
Previously Firefox used TraceMonkey, then TraceMonkey+JaegerMonkey, and now JaegerMonkey+Type Inference. The plan is to move to IonMonkey+Type Inference (not sure where JaegerMonkey fits into that).