Mozilla didn’t make them implement a browser feature that is not widely available. Believe it or not there are plenty of better soldering irons that don’t require a web browser to configure.
You don't have to have Chrome to configure it (the story talks about this). It's configured over a serial interface and among browsers only Chrome on desktop implements WebSerial (and probably other browsers based on Chrome). That said, they did go out of their way and make the Chrome experience nice.