Browsers have replaced their optimizing backends entirely a few times already. They all optimize similar kinds of code, but the details of when and how change a

Browsers have replaced their optimizing backends entirely a few times already. They all optimize similar kinds of code, but the details of when and how change all the time. Vendors have deprecated and regressed on whole benchmark suites when they've decided the tests no longer represent what they want to optimize for. The biggest problem is that JIT is guided by heuristics. Observations from interpreters decide when code is advanced to higher optimization tiers, and that varies between implementations and changes relatively often. Your hottest code is also subject to JIT cache pressue and eviction policy, so you can't even rely on it staying hot across different machines using the exact same browser.