Firefox UA string will contain Intel on ARM-based Macs and 10.16 on macOS Big Sur


Categories: DOM, Networking

Releases: Firefox 81


The user agent (UA) string of Firefox for macOS will make special cases for upcoming Mac computers with an ARM64-based processor and macOS 11 Big Sur to maintain web compatibility, just like Safari does.

  • The processor name will always be Intel
  • The OS version number will be represented as 10.16 instead of 11.0
  • The legacy OS name Mac OS X will also be retained

This measure applies to the User-Agent HTTP request header as well as relevant DOM properties. The complete UA string of Firefox 81 on Big Sur will be:

Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:81.0) Gecko/20100101 Firefox/81.0

And, navigator.oscpu will return Intel Mac OS X 10.16 while navigator.platform will always return MacIntel, preventing common UA detection code like this from being broken:

const isMac = navigator.platform === 'MacIntel';