|Name||Type||Garbage Collection||Security||Implemented In|
|Rhino||Compiler and interpreter||Java runtime||SecuritySupport interface, domain-based||Java|
|SpiderMonkey||Compiler and interpreter||Mark-and-Sweep, non-conservative (exact) collector||Java principals security model||C|
|V8||Virtual machine||Generational stop-the-world collector||Context-based, with security tokens||C++|
SpiderMonkey 1.8.1 has a just-in-time compiler that can convert bytecode into machine code to improve performance. This was contributed by Adobe and now co-maintained by Mozilla. The JIT watches for commonly executed code and attempts to optimise the equivalent native code. The Tracing JIT page on Mozilla’s site has more details.