With the native build, this second translation is avoided completely and we’re back to having a snappy browser. On startup, the JIT has to translate the JavaScript to machine code and while this is typically a very fast operation when running under emulation Rosetta has to then translate this JIT-generated machine code to machine code for another architecture.Īpple introduced a translation cache that likely removes this overhead completely for most applications but it does not work for code that is output by a JIT. One reasonable explanation for this faster startup could be that many parts of Firefox itself are written in the web’s own languages – JavaScript, CSS, and HTML – and thus use a JavaScript JIT for much of its own functionality. While most benchmarking of Apple Silicon indicated that the performance impact of Rosetta emulation was typically low and that applications could be expected to run at about 70-80% of native performance, we saw much larger gains when testing the native Firefox build, including doubled performance on some key benchmarks and a spectacular 2.5 times faster startup. Mozilla hit a couple new macos quirks, but they have already done most of the multiarch legwork before.Īnyways they mentioned emulation performance… Firefox was already built to be portable, including on ARM.

Firefox for macbook m1