I want to install Firefox on my mobile macOS

You mean iPhone ???

ios

See top menu Community forums there is a forum for the iPhone (ios)

I want to install Firefox on my mobile macOS

You mean on iOS/iPadOS as macOS refers to the OS used on Mac desktop and laptops.

See https://support.mozilla.org/en-US/kb/install-firefox-your-ipad-iphone-or-ipod

See top menu Community forums there is a forum for the iPhone (ios)

The thread is in the Firefox for iOS section ;)

Firefox for iOS on your mobile device seems to be working just fine since you posted this question from its rather recent version, so if you have any specific question in mind related to its use, you might want to elaborate a bit more.

If you're looking how to install desktop Firefox on macOS, there's a guide here: How to download and install Firefox on Mac