I know you jest, but I don't think that's a good example of "contrast" between the engines. That was just a bug/oversight and fixed in a couple of weeks after it was reported [1].

[1]: https://trac.webkit.org/changeset/269115/webkit

YMMV, but I find that Safari uses dramatically fewer local resources on my computer than Chrome does, for the same workload. Chrome can’t remotely handle the number of tabs I typically keep open (it chews up all available memory, and hangs or crashes). Even for lighter browsing usage, Chrome chews battery faster and slows the rest of my computer down. Overall Safari is the most usable, followed by Firefox.

In various numerical computing in Javascript projects/experiments I’ve done, Safari is typically fastest, but not always. At any rate, it is clear that all of these teams have done very extensive optimization work, and all of the modern browsers are engineering marvels.

But there are a lot of weird nooks and corners in all of the browsers when it comes to Javascript performance.