To confirm if you are on the native ARM build, type about:support in the address bar and you should see a suggestion below saying Rosetta Translated as “false”. Once done, restart the browser and it should be updated. Go to Menu > Help > About Firefox and you'll see the option to update to version 84. The update process is the same as before. Mozilla claims version 84 launches over 2.5x faster and web apps are 2x as responsive compared to version 83.
Running natively means it can fully benefit from the performance of the new architecture and the processing power of the M1 chip. While the previous version did still work on these newer machines, it would run under emulation through Rosetta whereas version 84 runs natively. Starting with version 84, the macOS build of Firefox will now natively support both Intel x86 and the ARM-based Apple Silicon processors, including the current M1 SoC and all future models. The big news with this version is that it adds support for Apple Silicon on the macOS version, making it the third browser after Safari and Chrome to do so. Mozilla has released version 84 of Firefox across all three desktop platforms.
