It should be noted that some of those features can be disabled via environment variables: https://developer.mozilla.org/docs/Mozilla/Benchmarking https://devel

It should be noted that some of those features can be disabled via environment variables: https://developer.mozilla.org/docs/Mozilla/Benchmarking https://developer.mozilla.org/docs/Mozilla/Benchmarking Specifically, I use those environment variables: JS_OPTION_USE_UNBOXED_ARRAYS=1 JSGC_DISABLE_POISONING=1 There's at least one other thing (async stack) that I'm aware of that may be tunable: https://bugzilla.mozilla.org/show_bug.cgi?id=1280819 https://bugzilla.mozilla.org/show_bug.cgi?id=1280819 edit: just figured out that that's "javascript.options.asyncstack", so I set it to disabled on nightly too. Fwiw, the unboxed objects bug is: https://bugzilla.mozilla.org/show_bug.cgi?id=1153266 https://bugzilla.mozilla.org/show_bug.cgi?id=1153266 edit: typedobj performance improvements visible at the bottom of https://arewefastyet.com/#machine=28&view=breakdown&suite=misc https://arewefastyet.com/#machine=28&view=breakdown&suite=mi... edit: removed MOZ_QUIET=1, as a source inspection reveals that it is only compiled #ifdef DEBUG.