Since the research team who discovered the SplitSpectre attack used SpiderMonkey 52.7.4 — the JavaScript engine in Firefox — to target both Intel and AMD chips nobody seems to be safe anymore. The attack has been successfully carried out against Intel Haswell, Intel Skylake, and AMD Ryzen processors.
https://www.notebookcheck.net/The-phantom-returns-Researchers-discover-a-new-Spectre-CPU-attack-name-it-SplitSpectre.374046.0.html