mozilla gets no credit at all? According to some old zdnet benchmarks I could google up[1], their IE7's sunspider was result was 22678ms, Firefox 2's result was 12460ms, Firefox 3 RC1 2377ms. So mozilla managed to make their Firefox 3 js engine about 10 times faster than IE7 in sunspider, more than 5 times faster than Firefox 2. Safari at the time was pretty much on par with Firefox 3. That's before any public Google Chrome release (their first release was a few months after Firefox 3 stable). After the Chrome release, js perf mostly became an arms race between Google and mozilla with the other vendors trying to not be left too far behind in the dust.
Of course, in current gen browsers and on current gen hardware, sunspider is so fast it's more noise than measurement.
[1] https://www.zdnet.com/a/img/resize/3062e92bf2f9f018f49723939...
Full size image url is broken :P